Method and device for performing NIB CoMP transmission in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system, and more particularly, to a method and device for performing or supporting NIB coordinated multi-point (CoMP) transmission in a wireless communication system. The method and device for performing NIB CoMP transmission in the wireless communication system according to an embodiment of the present invention include: receiving signaling comprising at least one CoMP hypothesis set and at least one benefit metric from a first network node, at a second network node; and performing CoMP transmission based on the at least one CoMP hypothesis set, at the second network node. The at least one CoMP hypothesis set comprises information on hypothetical operation of CoMP network nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2014/006942, filed on Jul. 29, 2014,which claims the benefit of U.S. Provisional Application No. 61/859,762,filed on Jul. 29, 2013, 61/912,007, filed on Dec. 4, 2013, 61/926,380,filed on Jan. 12, 2014, 61/927,968, filed on Jan. 15, 2014, 61/929,966,filed on Jan. 21, 2014, 61/952,881, filed on Mar. 14, 2014, 61/968,976,filed on Mar. 21, 2014 and 61/972,425, filed on Mar. 31, 2014, thecontents of which are all hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system and,more particularly, to a method and device for performing or supportingNIB CoMP transmission in a wireless communication system.

BACKGROUND ART

Multiple-Input Multiple-Output (MIMO) is a technology for improvingefficiency of data transmission and reception using multiple transmitantennas and multiple receive antennas rather than using one transmitantenna and one receive antenna. If a single antenna is used, a receiveentity receives data through a single antenna path. In contrast, ifmultiple antennas are used, the receive entity receives data throughseveral paths, accordingly data transmission rate and throughput may beimproved, and the coverage may be extended.

To increase multiplexing gain of the MIMO operation, an MIMO transmitentity may use channel state information (CSI) fed back by the MIMOreceive entity. The receive entity may determine the CSI by performingchannel measurement using a predetermined reference signal (RS) from thetransmit entity.

Research has been actively conducted on a coordinated multi-point (CoMP)system for improving throughput for a user at the cell boundary byapplying improved MIMO transmission in a multi-cell environment. Withthe CoMP system, inter-cell interference may be reduced in themulti-cell environment, and overall system performance may be improved.For example, CoMP techniques include joint processing (JP) of performingcommon computational processing between neighboring cells by groupingmultiple neighboring cells and considering the same as a virtual MIMOsystem and cooperative beamforming (C-BF) capable of solving the problemof inter-cell interference by adjusting a beam pattern betweenneighboring cells.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method for accurately and efficiently performing or supporting CoMPoperation when delay is present in signal transmission and receptionbetween points participating in CoMP (in, for example, a non-idealbackhaul (NIB) network).

It is to be understood that technical objects to be achieved by thepresent invention are not limited to the aforementioned technicalobjects and other technical objects which are not mentioned herein willbe apparent from the following description to one of ordinary skill inthe art to which the present invention pertains.

Technical Solution

The object of the present invention can be achieved by providing amethod for performing coordinated multi-point (CoMP) transmission on awireless communication network, the method including transmitting firsttype signaling from a first network node to a second network node, thefirst type signaling containing one or more first CoMP hypothesis setsand one or more first benefit metrics, and receiving, at the firstnetwork node, second type signaling from the second network node, thesecond type signaling containing one or more second CoMP hypothesis setsand one or more second benefit metrics. At least one of the first typesignaling and the second type signaling may further contain one or moresets of CSI information about one or more user equipments (UEs), the oneor more sets of the CSI information including CSI information generatedaccording to each channel state information (CSI)-process index, TheCSI-process index may be defined as a value uniquely identified on thewireless communication network.

In another aspect of the present invention, provided herein is a networknode for performing coordinated multi-point (CoMP) transmission on awireless communication network, the network node device including atransceiver, and a processor, wherein the processor is configured totransmit first type signaling from the network node to another networknode using the transceiver, the first type signaling containing one ormore first CoMP hypothesis sets and one or more first benefit metrics,and receive, at the network node, second type signaling from the secondnetwork node using the transceiver, the second type signaling containingone or more second CoMP hypothesis sets and one or more second benefitmetrics. Each of the one or more first or second CoMP hypothesis setsmay include information about a transmission assumption for each of theCoMP network nodes according to each channel state information(CSI)-process index. The CSI-process index may be defined as a valueuniquely identified on the wireless communication network.

The above aspects of the present invention may include the followingdetails.

The CSI-process index may correspond to a combination of a non-zeropower (NZP) CSI-reference signal (RS) index and a CSI-interferencemeasurement (IM) index, wherein the NZP CSI-RS index may be defined as avalue uniquely identified on the wireless communication network, and theCSI-IM index may be defined as a value uniquely defined on the wirelesscommunication network.

Each of the one or more first or second CoMP hypothesis sets may beassociated with one benefit metric, wherein the benefit metric may havea quantized value of a benefit expected for CoMP transmission schedulingon an assumption of a CoMP hypothesis set associated therewith.

Each of the one or more first or second CoMP hypothesis sets may includean identifier (ID) of each of the CoMP network nodes and informationabout a transmission assumption for each of the CoMP network nodes.

A transmission assumption for each of the CoMP network nodes may includeat least one of whether to perform muting, a transmit power level andprecoding information.

At least one of the first type signaling and the second type signalingmay contain information indicating at least one of a time interval and afrequency band, the time interval and frequency band being related tothe CoMP transmission.

The information indicating the time interval may include informationabout a frame number, the CoMP transmission starting at the framenumber.

The information indicating the frequency band may include informationabout subbands, the CoMP transmission being performed in the subbands,wherein each of the subbands may include a plurality of resource blocks(RBs), wherein a size of each of the subbands may increase when a systembandwidth increases.

At least one of the first type signaling and the second type signalingmay include at least one of one or more measurement reports on a set ofthe UEs, an SRS reception power for the set of the UEs, a user perceivedthroughput for the set of the UEs, and transmit power information, thetransmit power information being defined in one or more domains offrequency, time, power and space domains with respect to at least one ofthe CoMP network nodes.

A link between the CoMP network nodes may be a non-ideal backhaul (NIB)link.

An interface between the CoMP network nodes may be an X2 interface.

The above general description and the following detailed description ofthe present invention are exemplarily given to supplement therecitations in the claims.

Advantageous Effects

According to embodiments of the present invention, a method foraccurately and efficiently performing or supporting CoMP operation whendelay is present in signal transmission and reception between pointsparticipating in CoMP (in, for example, an NIB network) may be provided.

It will be appreciated by those skilled in the art that the effects thatcan be achieved with the present invention are not limited to what hasbeen described above and other advantages of the present invention willbe clearly understood from the following detailed description taken inconjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a radio frame structure;

FIG. 2 is a diagram illustrating a resource grid for one downlink (DL)slot;

FIG. 3 is a diagram illustrating a DL subframe structure;

FIG. 4 is a diagram illustrating an uplink (UL) subframe structure;

FIG. 5 illustrates configuration of a wireless communication systemhaving multiple antennas;

FIG. 6 is a diagram illustrating an exemplary pattern of a CRS and a DRSon one RB pair;

FIG. 7 is a diagram illustrating an exemplary DMRS pattern defined inLTE-A;

FIG. 8 is a diagram illustrating exemplary CSI-RS patterns defined inLTE-A;

FIG. 9 is a diagram illustrating an exemplary scheme in which a CSI-RSis periodically transmitted;

FIG. 10 illustrates an exemplary downlink CoMP operation;

FIG. 11 illustrates a situation in which CoMP is not applied;

FIG. 12 illustrates an SSPM technique;

FIG. 13 illustrates a benefit metric signaled together with a CoMPhypothesis for a frequency/time resource map;

FIG. 14 illustrates an improved RNTP map (or improved ABS map) signaledwith respect to a frequency/time resource;

FIG. 15 illustrates a benefit metric signaled together with a CoMPhypothesis for a frequency/time resource map;

FIG. 16 illustrates a CB technique;

FIG. 17 is a flowchart illustrating a signaling method according to anembodiment of the present invention; and

FIG. 18 is a diagram illustrating configuration of a preferredembodiment of a network node of the present invention.

BEST MODE

The following embodiments may correspond to combinations of elements andfeatures of the present invention in prescribed forms. And, it may beable to consider that the respective elements or features may beselective unless they are explicitly mentioned. Each of the elements orfeatures may be implemented in a form failing to be combined with otherelements or features. Moreover, it may be able to implement anembodiment of the present invention by combining elements and/orfeatures together in part. A sequence of operations explained for eachembodiment of the present invention may be modified. Some configurationsor features of one embodiment may be included in another embodiment ormay be substituted for corresponding configurations or features ofanother embodiment.

In this specification, embodiments of the present invention aredescribed centering on the data transmission/reception relations betweena base station and a user equipment. In this case, a base station has ameaning of a terminal node of a network directly communicating with auser equipment. In this disclosure, a specific operation explained asperformed by a base station may be performed by an upper node of thebase station in some cases.

In particular, in a network constructed with a plurality of networknodes including a base station, it is apparent that various operationsperformed for communication with a user equipment may be performed by abase station or other network nodes except the base station. ‘Basestation (BS)’ may be substituted with such a terminology as a fixedstation, a Node B, an eNode B (eNB), an access point (AP), Remote RadioHead (RRD), Transmission point (TP), Reception Point (RP) and the like.A relay may be substituted with such a terminology as a relay node (RN),a relay station (RS), and the like. And, ‘terminal’ may be substitutedwith such a terminology as a user equipment (UE), an MS (mobilestation), an MSS (mobile subscriber station), an SS (subscriberstation), or the like.

Specific terminologies used in the following description are provided tohelp understand the present invention and the use of the specificterminologies may be modified into a different form in a range of notdeviating from the technical idea of the present invention.

Occasionally, to prevent the present invention from getting vaguer,structures and/or devices known to the public are skipped or may berepresented as block diagrams centering on the core functions of thestructures and/or devices. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of wireless access systems includingIEEE 802 system, 3GPP system, 3GPP LTE system, 3GPP LTE-A (LTE-Advanced)system and 3GPP2 system. In particular, the steps or parts, which arenot explained to clearly reveal the technical idea of the presentinvention, in the embodiments of the present invention may be supportedby the above documents. Moreover, all terminologies disclosed in thisdocument may be supported by the above standard documents.

The following description of embodiments of the present invention may beusable for various wireless access systems including CDMA (code divisionmultiple access), FDMA (frequency division multiple access), TDMA (timedivision multiple access), OFDMA (orthogonal frequency division multipleaccess), SC-FDMA (single carrier frequency division multiple access) andthe like. CDMA may be implemented with such a radio technology as UTRA(universal terrestrial radio access), CDMA 2000 and the like. TDMA maybe implemented with such a radio technology as GSM/GPRS/EDGE (GlobalSystem for Mobile communications)/General Packet Radio Service/EnhancedData Rates for GSM Evolution). OFDMA may be implemented with such aradio technology as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, E-UTRA (Evolved UTRA), etc. UTRA is a part of UMTS (UniversalMobile Telecommunications System). 3GPP (3rd Generation PartnershipProject) LTE (long term evolution) is a part of E-UMTS (Evolved UMTS)that uses E-UTRA. The 3GPP LTE adopts OFDMA in downlink (hereinafterabbreviated DL) and SC-FDMA in uplink (hereinafter abbreviated UL). And,LTE-A (LTE-Advanced) is an evolved version of 3GPP LTE. WiMAX may beexplained by IEEE 802.16e standard (e.g., WirelessMAN-OFDMA referencesystem) and advanced IEEE 802.16m standard (e.g., WirelessMAN-OFDMAadvanced system). For clarity, the following description mainly concerns3GPP LTE and LTE-A standards, by which the technical idea of the presentinvention may be non-limited.

FIG. 1 is a diagram for a structure for a radio frame of 3GPP LTEsystem.

In a cellular OFDM (orthogonal frequency division multiplex) radiopacket communication system, UL/DL (uplink/downlink) data packettransmission is performed by a unit of subframe. And, one subframe isdefined as a predetermined time interval including a plurality of OFDMsymbols. In the 3GPP LTE standard, a type 1 radio frame structureapplicable to FDD (frequency division duplex) and a type 2 radio framestructure applicable to TDD (time division duplex) are supported.

FIG. 1 (a) is a diagram for a structure of a type 1 radio frame. A DL(downlink) radio frame includes 10 subframes. Each of the subframesincludes 2 slots in time domain. And, a time taken to transmit onesubframe is defined as a transmission time interval (hereinafterabbreviated TTI). For instance, one subframe may have a length of 1 msand one slot may have a length of 0.5 ms. One slot may include aplurality of OFDM symbols in time domain and may include a plurality ofresource blocks (RBs) in frequency domain. Since 3GPP LTE system usesOFDMA in downlink, OFDM symbol is provided to indicate one symbolinterval. The OFDM symbol may be named SC-FDMA symbol or symbolinterval. Resource block (RB) is a resource allocation unit and mayinclude a plurality of contiguous subcarriers in one slot.

The number of OFDM symbols included in one slot may vary in accordancewith a configuration of CP (cyclic prefix). The CP may be categorizedinto an extended CP and a normal CP. For instance, in case that OFDMsymbols are configured by the normal CP, the number of OFDM symbolsincluded in one slot may correspond to 7. In case that OFDM symbols areconfigured by the extended CP, since a length of one OFDM symbolincreases, the number of OFDM symbols included in one slot may besmaller than that of the case of the normal CP. In case of the extendedCP, for instance, the number of OFDM symbols included in one slot maycorrespond to 6. If a channel status is unstable (e.g., a UE is movingat high speed), it may be able to use the extended CP to further reducethe inter-symbol interference.

When the normal CP is used, each slot includes 7 OFDM symbols, and thuseach subframe includes 14 OFDM symbols. In this case, the first two orthree OFDM symbols of each subframe may be allocated to a physicaldownlink control channel (PDCCH) and the other three OFDM symbols may beallocated to a physical downlink shared channel (PDSCH).

FIG. 1 (b) is a diagram for a structure of a downlink radio frame oftype 2. A type 2 radio frame includes 2 half frames. Each of the halfframe includes 5 subframes, a DwPTS (downlink pilot time slot), a GP(guard period), and an UpPTS (uplink pilot time slot). Each of thesubframes includes 2 slots. Subframe consisting of DwPTS, GP and UpPTSrefers to special subframe. The DwPTS is used for initial cell search,synchronization, or a channel estimation in a user equipment. The UpPTSis used for channel estimation of a base station and matching atransmission synchronization of a user equipment. The guard period is aperiod for eliminating interference generated in uplink due tomulti-path delay of a downlink signal between uplink and downlink.Meanwhile, one subframe includes 2 slots irrespective of a type of aradio frame.

The above-described structures of the radio frame are exemplary only.And, the number of subframes included in a radio frame, the number ofslots included in the subframe and the number of symbols included in theslot may be modified in various ways.

FIG. 2 is a diagram for a resource grid in a downlink slot.

Referring to FIG. 2, one downlink (DL) slot includes 7 OFDM symbols intime domain and one resource block (RB) includes 12 subcarriers infrequency domain, by which the present invention may be non-limited. Forinstance, in case of a normal CP (Cyclic Prefix), one slot includes 7OFDM symbols. In case of an extended CP, one slot may include 6 OFDMsymbols. Each element on a resource grid is called a resource element.One resource block includes 12×7 resource elements. The number N^(DL) ofresource blocks included in a DL slot may depend on a DL transmissionbandwidth. And, the structure of an uplink (UL) slot may be identical tothat of the DL slot.

FIG. 3 is a diagram for a structure of a downlink (DL) subframe.

A maximum of 3 OFDM symbols situated in a head part of a first slot ofone subframe correspond to a control region to which control channelsare assigned. The rest of OFDM symbols correspond to a data region towhich PDSCH (physical downlink shared channel) is assigned.

Examples of DL control channels used by 3GPP LTE system may includePCFICH (Physical Control Format Indicator Channel), PDCCH (PhysicalDownlink Control Channel), PHICH (Physical hybrid automatic repeatrequest indicator Channel) and the like. The PCFICH is transmitted in afirst OFDM symbol of a subframe and includes information on the numberof OFDM symbols used for a transmission of a control channel within thesubframe. The PHICH is a response channel in response to UL transmissionand includes an ACK/NACK signal. Control information carried on PDCCHmay be called downlink control information (hereinafter abbreviatedDCI). The DCI may include UL scheduling information, DL schedulinginformation or a UL transmit power control command for a random UE (userequipment) group. PDCCH is able to carry resource allocation andtransmission format (or called a DL grant) of DL-SCH (downlink sharedchannel), resource allocation information (or called a UL grant) ofUL-SCH (uplink shared channel), paging information on PCH (pagingchannel), system information on DL-SCH, resource allocation to an upperlayer control message such as a random access response transmitted onPDSCH, a set of transmission power control commands for individual userequipments within a random user equipment (UE) group, activation of VoIP(voice over IP) and the like. A plurality of PDCCHs may be transmittedin a control region and a user equipment is able to monitor a pluralityof the PDCCHs.

PDCCH is configured with the aggregation of at least one or morecontiguous CCEs (control channel elements). CCE is a logical assignmentunit used to provide PDCCH with a code rate in accordance with a stateof a radio channel. CCE corresponds to a plurality of REGs (resourceelement groups). A format of PDCCH and the number of bits of anavailable PDCCH are determined depending on correlation between thenumber of CCEs and a code rate provided by the CCEs.

A base station determines PDCCH format in accordance with DCI totransmit to a user equipment and attaches CRC (cyclic redundancy check)to control information. The CRC is masked with a unique identifier(called RNTI (radio network temporary identifier) in accordance with anowner or usage of PDCCH. If the PDCCH is provided for a specific userequipment, the CRC may be masked with a unique identifier of the userequipment, i.e., C-RNTI (i.e., Cell-RNTI). If the PDCCH is provided fora paging message, the CRC may be masked with a paging indicationidentifier (e.g., P-RNTI (Paging-RNTI)). If the PDCCH is provided forsystem information, and more particularly, for a system informationblock (SIB), the CRC may be masked with a system information identifier(e.g., SI-RNTI (system information-RNTI). In order to indicate a randomaccess response that is a response to a transmission of a random accesspreamble of a user equipment, CRC may be masked with RA-RNTI (randomaccess-RNTI).

FIG. 4 is a diagram for a structure of an uplink (UL) subframe.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in frequency domain. A physical UL control channel(PUCCH), which includes UL control information, is assigned to thecontrol region. And, a physical UL shared channel (PUSCH), whichincludes user data, is assigned to the data region. In order to maintainsingle carrier property, one user equipment does not transmit PUCCH andPUSCH simultaneously. PUCCH for one user equipment is assigned to aresource block pair (RB pair) in a subframe. Resource blocks belongingto the resource block (RB) pair may occupy different subcarriers in eachof 2 slots. Namely, a resource block pair allocated to PUCCH isfrequency-hopped on a slot boundary.

Modeling of MIMO System

FIG. 5 illustrates configuration of a wireless communication systemhaving multiple antennas.

Referring to FIG. 5(a), if the number of transmit (Tx) antennasincreases to NT, and the number of receive (Rx) antennas increases toNR, a theoretical channel transmission capacity of the wirelesscommunication system increases in proportion to the number of antennas,differently from a case in which only a transmitter or receiver usesmultiple antennas, and accordingly transmission rate and frequencyefficiency may be significantly increased. In this case, the transferrate acquired by the increased channel transmission capacity may betheoretically increased by a predetermined amount that corresponds tomultiplication of a maximum transfer rate (Ro) acquired when one antennais used by a rate of increase (Ri). The rate of increase (Ri) may berepresented by the following Equation 1.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For example, provided that a MIMO system uses four Tx antennas and fourRx antennas, the MIMO system may theoretically acquire a high transferrate which is four times that of a single antenna system. After theabove-mentioned theoretical capacity increase of the MIMO system wasdemonstrated in the mid-1990s, many developers began to conductintensive research into a variety of technologies which maysubstantially increase data transfer rate using the theoretical capacityincrease. Some of the above technologies have been adopted in a varietyof wireless communication standards such as, for example,third-generation mobile communication and next-generation wireless LAN.

A variety of MIMO-associated technologies have been intensivelyresearched. For example, research into information theory associatedwith MIMO communication capacity under various channel environments ormultiple access environments, research into radio frequency (RF) channelmeasurement and modeling of the MIMO system, and research intospace-time signal processing technology have been conducted.

Mathematical modeling of a communication method for use in theaforementioned MIMO system will hereinafter be described in detail. Itis assumed that the system includes N_(T) Tx antennas and N_(R) Rxantennas.

In the case of a transmission signal, the maximum number of pieces oftransmittable information is N_(T) under the condition that N_(T) Txantennas are used, and the transmission information may be representedby the following equation.s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Equation 2]

Individual pieces of transmission information s₁, s₂, . . . , s_(NT) mayhave different transmit powers. In this case, if the individual transmitpowers are denoted by P₁, P₂, . . . , P_(NT), transmission informationhaving an adjusted transmit power may be represented by the followingequation.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

Ŝ may be represented by the following equation using a diagonal matrix Pof transmit powers.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

Suppose that a weight matrix W is applied to the information vector Ŝfor which transmit powers have been adjusted, thereby N_(T) transmissionsignals x₁, x₂, . . . , x_(NT) to be actually transmitted areconfigured. The weight matrix W serves to properly distributetransmission information to individual antennas according totransmission channel situations. The above-mentioned transmissionsignals x₁, x₂, . . . , x_(NT) may be represented by the followingequation using vector X.

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {\quad{{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1\; N_{T}} \\w_{21} & w_{22} & \ldots & w_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

Here, W_(ij) denotes a weight corresponding to the i-th Tx antenna andthe j-th information. W is also called a precoding matrix.

When N_(R) Rx antennas are used, received signals y₁, y₂, . . . , y_(NR)of individual antennas may be represented by a vector shown in thefollowing equation.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

When channel modeling is executed in the MIMO communication system,individual channels may be distinguished from each other according toTx/Rx antenna indexes. A specific channel from a Tx antenna j to an Rxantenna i is denoted by h_(ij). Regarding h_(ij), it should be notedthat an Rx antenna index is located ahead of a Tx antenna index.

FIG. 5(b) shows channels from N_(T) Tx antennas to Rx antenna i. Thechannels may be represented in the form of a vector or matrix. Referringto FIG. 5(b), the channels from the N_(T) Tx antennas to the Rx antennai may be represented by the following equation.h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

All channels from the N_(T) Tx antennas to N_(R) Rx antennas may also berepresented as the following.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Additive white Gaussian noise (AWGN) is added to an actual channel afterapplication of a channel matrix H. AWGN n₁, n₂, . . . , n_(NR) added toeach of N_(R) Rx antennas may be represented by the following equation.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Reception signal calculated by the mathematical modeling described abovemay be represented by the following equation.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

The number of rows and the number of columns of channel matrix Hindicating a channel condition are determined by the number of Tx/Rxantennas. In the channel matrix H, the number of rows is equal to thenumber (N_(R)) of Rx antennas, and the number of columns is equal to thenumber (N_(T)) of Tx antennas. Namely, the channel matrix H is denotedby an N_(R)×N_(T) matrix.

A rank of a matrix is defined by the smaller of the number of rows andthe number of columns, in which the rows and the columns are independentof each other. Therefore, the matrix rank may not be higher than thenumber of rows or columns. The rank of the channel matrix H may berepresented by the following equation.rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

The rank may be defined as the number of non-zero Eigen values whenEigen value decomposition is performed on the matrix. Similarly, therank may be defined as the number of non-zero singular values whensingular value decomposition is performed on the matrix. Accordingly,the rank of the channel matrix refers to a maximum number of pieces ofinformation that may be transmitted on a given channel.

In this specification, “rank” with respect to MIMO transmissionindicates the number of paths through which signals may be independentlytransmitted at specific time in a specific frequency resource and “thenumber of layers” refers to the number of signal streams transmittedthrough each path. Since a transmitter transmits as many layers as therank used in signal transmission, the rank corresponds to the number oflayers unless otherwise mentioned.

Reference Signal (RS)

When a packet is transmitted in a wireless communication system, sincethe packet is transmitted via a radio channel, a signal may be distortedin the course of transmission. In order for a receiving end to correctlyreceive a distorted signal, it may be preferable that the distorted andreceived signal is corrected using channel information. In order to findout the channel information, a signal known to both of a transmittingend and the receiving end is transmitted and finds out the channelinformation with the extent of distortion when the signal is received ona channel. The signal is called a pilot signal or a reference signal.

When a data is transmitted/received using MIMO antenna, it may bepreferable that a channel state between a transmitting antenna and areceiving antenna is detected in order for a receiving end to correctlyreceive the data. Hence, in order for the receiving end to detect thechannel state, each transmitting antenna of the transmitting end maypreferably have an individual reference signal.

In a wireless communication system, RSs may be broadly divided into twotypes according to the purposes thereof. One type is used to acquirechannel information and the other type is used for data demodulation.Since the former RS is used to allow the UE to acquire DL channelinformation, this RS should be transmitted over a wide band, and even aUE which does not receive DL data in a specific subframe should receiveand measure the RS. Such RS is also used for measurement of, forexample, handover. The latter RS is sent when an eNB sends a resource ondownlink. The UE may perform channel measurement by receiving this RS,thereby implementing data modulation. This RS should be transmitted in aregion in which data is transmitted.

Legacy 3GPP LTE systems (e.g., 3GPP LTE Release-8) define two types ofdownlink RSs for the unicast service. One is a common RS (CRS), and theother is a dedicated RS (DRS). The CRS is used for acquisition ofinformation about the channel state and measurement of, for example,handover, and may be referred to as a cell-specific RS. The DRS is usedfor data demodulation, and may be referred to as a UE-specific RS. Inthe legacy 3GPP LTE systems, the DRS may be used only for datademodulation, and the CRS may be used for both acquisition of channelinformation and data demodulation.

The CRS is transmitted cell-specifically in every subframe in awideband. The CRS may be transmitted with respect to up to four antennaports depending on the number of Tx antennas of the eNB. For example, ifthe number of Tx antennas of the eNB is 2, CRSs for antenna ports #0 and#1 are transmitted. If the number of Tx antennas of the eNB is 4, CRSsfor antenna ports #0 to #3 are respectively transmitted.

FIG. 6 is a diagram for an exemplary pattern of CRS and DRS on aresource block (RB) pair.

As an example of reference signal pattern, FIG. 6 shows a pattern of CRSand DRS on a RB pair (normap CP case, 14 OFDM symbol in time domain×12subcarriers in frequency domain) in a system supporting 4 antennas by abase station. In FIG. 6, resource elements (RE) represented as ‘R0’,‘R1’, ‘R2’, and ‘R3’ indicate positions of the CRS for an antenna port0, 1, 2, and 3, respectively. Meanwhile, resource elements representedas ‘ID’ in FIG. 6 indicates positions of the DRS.

LTE-A, which is an advanced version of LTE, can support up to 8 Txantennas on downlink. Accordingly, RSs for up to 8 Tx antennas need tobe supported in LTE-A. In LTE, downlink RSs are defined only for up to 4antenna ports. Therefore, if an eNB has 4 to 8 DL Tx antennas in LTE-A,RSs for these antenna ports need to be additionally defined. As the RSsfor up to 8 Tx antenna ports, both the RS for channel measurement andthe RS for data demodulation need to be considered.

One important consideration in designing an LTE-A system is backwardcompatibility. Backward compatibility refers to supporting the legacyLTE UE such that the legacy LTE UE normally operates in the LTE-Asystem. In terms of RS transmission, if RSs for up to 8 Tx antennas areadded to a time-frequency region in which a CRS defined in the LTEstandard is transmitted in every subframe over the full band, RSoverhead excessively increases. Accordingly, in designing new RSs for upto 8 antenna ports, reduction in RS overhead needs to be considered.

The new RSs introduced in LTE-A may be classified into two types. One isa channel state information-RS (CSI-RS) intended for channel measurementfor selecting a transmission rank, a modulation and coding scheme (MCS),a precoding matrix index (PMI), and the like, and the other is ademodulation RS (DMRS) intended for demodulation of data transmittedthrough up to 8 Tx antennas.

The CSI-RS intended for channel measurement is designed only for channelmeasurement, unlike the existing CRS, which is used for datademodulation as well as for channel measurement and handovermeasurement. Of course, the CSI-RS may also be used for handovermeasurement. Since the CSI-RS is transmitted only in order to obtaininformation about channel states, the CSI-RS need not be transmitted inevery subframe, unlike the CRS for the legacy LTE system. Accordingly,to reduce overhead of the CSI-RS, the CSI-RS may be designed to beintermittently (e.g., periodically) transmitted in the time domain.

When data is transmitted in a certain DL subframe, a dedicated DMRS istransmitted to a UE for which data transmission is scheduled. That is,the DMRS may be referred to as a UE-specific RS. A DMRS dedicated to aspecific UE may be designed to be transmitted only in a resource regionin which the UE is scheduled, i.e., the time-frequency region in whichdata for the UE is transmitted.

FIG. 7 is a diagram for an example of a DMRS pattern defined in LTE-Asystem.

FIG. 7 shows a position of a resource element to which a DMRS istransmitted on one resource block pair (in case of a normal CP, 14 OFDMsymbols in time domain×12 subcarriers in frequency domain) in which DLdata is transmitted. The DMRS may be transmitted in response to 8antenna ports (antenna port index 7, 8, 9, 10) additionally defined inLTE-A system. The DMRS for antenna ports different from each other maybe distinguished from each other in a manner of being positioned atfrequency resources (subcarriers) different from each other and/or timeresources (OFDM symbols) different from each other (i.e., the DM RS forantenna ports different from each other may be multiplexed by FDM and/orTDM scheme). And, the DMRS for antenna ports different from each otherpositioned at an identical time-frequency resource may be distinguishedfrom each other by an orthogonal code (i.e., the DMRS for antenna portsdifferent from each other may be multiplexed by CDM scheme). In theexample of FIG. 7, DMRSs for antenna ports 7 and 8 may be positioned onthe REs indicated by DMRS CDM Group 1 and be multiplexed by anorthogonal code. Similarly, in the example of FIG. 7, DMRSs for antennaports 9 and 10 may be positioned on the REs indicated by DMRS Group 2and be multiplexed by the orthogonal code.

When the eNB transmits a DMRS, precoding applied to data is applied tothe DMRS. Accordingly, the channel information estimated by the UE usingthe DMRS (or UE-specific RS) is precoded channel information. The UE mayeasily perform data demodulation using the precoded channel informationestimated through the DMRS. However, the UE does not know theinformation about the precoding applied to the DMRS, and accordingly theUE may not acquire, from the DMRS, channel information that is notprecoded. The UE may acquire the channel information that is notprecoded, using an RS separate from the DMRS, namely using the CSI-RSmentioned above.

FIG. 8 is a diagram for examples of a CSI-RS pattern defined in LTE-Asystem.

FIG. 8 shows a position of a resource element to which a CSI-RS istransmitted on one resource block pair (in case of a normal CP, 14 OFDMsymbols in time domain×12 subcarriers in frequency domain) in which DLdata is transmitted. One CSI-RS pattern among patterns depicted in FIG.8 (a) to FIG. 8 (e) may be used in a prescribed DL subframe. The CSI-RSmay be transmitted in response to 8 antenna ports (antenna port index15, 16, 17, 18, 19, 20, 21 and 22) additionally defined in LTE-A system.The CSI-RS for antenna ports different from each other may bedistinguished from each other in a manner of being positioned atfrequency resources (subcarriers) different from each other and/or timeresources (OFDM symbols) different from each other (i.e., the CSI-RS forantenna ports different from each other may be multiplexed by FDM and/orTDM scheme). And, the CSI-RS for antenna ports different from each otherpositioned at an identical time-frequency resource may be distinguishedfrom each other by an orthogonal code (i.e., the CSI-RS for antennaports different from each other may be multiplexed by CDM scheme).Referring to the example of FIG. 8 (a), CSI-RSs for an antenna port 15and 16 may be positioned at resource elements (REs) represented as aCSI-RS CDM group 1 and the CSI-RSs for the antenna port 15 and 16 may bemultiplexed by the orthogonal code. Referring to the example of FIG. 8(a), CSI-RSs for an antenna port 17 and 18 may be positioned at resourceelements (REs) represented as a CSI-RS CDM group 2 and the CSI-RSs forthe antenna port 17 and 18 may be multiplexed by the orthogonal code.Referring to the example of FIG. 7 (a), CSI-RSs for an antenna port 19and 20 may be positioned at resource elements (REs) represented as aCSI-RS CDM group 3 and the CSI-RSs for the antenna port 19 and 20 may bemultiplexed by the orthogonal code. Referring to the example of FIG. 8(a), CSI-RSs for an antenna port 21 and 22 may be positioned at resourceelements (REs) represented as a CSI-RS CDM group 4 and the CSI-RSs forthe antenna port 21 and 22 may be multiplexed by the orthogonal code. Aprinciple explained on the basis of FIG. 8 (a) may be identicallyapplied to FIG. 8 (b) to FIG. 8 (e).

The RS patterns depicted in FIG. 6 to FIG. 8 are just examples. Variousexamples of the present invention may be non-limited to a specific RSpattern. In particular, in case of using an RS pattern different fromthe RS patterns depicted in FIG. 6 to FIG. 8, various embodiments of thepresent invention may also be identically applied to the RS pattern.

CSI-RS Configuration

As described above, in the LTE-A system supporting up to 8 Tx antennason downlink, an eNB needs to transmit CSI-RSs for all antenna ports.Since transmitting CSI-RSs for a maximum of 8 Tx antenna ports in everysubframe excessively increases overhead, the CSI-RS may need to beintermittently transmitted in the time domain to reduce overhead, ratherthan being transmitted in every subframe. Accordingly, the CSI-RS may beperiodically transmitted with a periodicity corresponding to an integermultiple of one subframe or transmitted in a specific transmissionpattern.

Here, the periodicity or pattern in which the CSI-RS is transmitted maybe configured by a network (e.g., an eNB). To perform CSI-RS-basedmeasurement, the UE should be aware of a CSI-RS configuration for eachCSI-RS antenna port of a cell (or a TP) to which the UE belongs. TheCSI-RS configuration may include the index of a downlink subframe inwhich a CSI-RS is transmitted, time-frequency positions (e.g., a CSI-RSpattern as shown in FIGS. 8(a) to 8(e)) of CSI-RS REs in a transmissionsubframe, and a CSI-RS sequence (which is a sequence that is intendedfor CSI-RS and is pseudo-randomly generated based on the slot number,cell ID, CP length and the like according to a predetermined rule). Thatis, a given eNB may use a plurality of CSI-RS configurations, and informUE(s) in a cell of CSI-RS configurations to be used for the UE(s) amongthe CSI-RS configurations.

The plurality of CSI-RS configurations may or may not include a CSI-RSconfiguration for which the UE assumes that the transmit power of theCSI-RS is non-zero. In addition, the plurality of CSI-RS configurationsmay or may not include at least one CSI-RS configuration for which theUE assumes that the transmit power of the CSI-RS is zero transmit power.

Further, each bit of a parameter (e.g., a 16-bit bitmap ZeroPowerCSI-RSparameter) for a CSI-RS configuration of zero transmit power may becaused by a higher layer to correspond to the CSI-RS configuration (orREs to which CSI-RSs can be allocated according to the CSI-RSconfiguration), and the UE may assume that the transmit power on theCSI-RS REs of a CSI-RS configuration corresponding to a bit set to 1 inthe parameter is 0.

Since CSI-RSs for the respective antenna ports need to be distinguishedfrom each other, resources on which the CSI-RSs for the antenna portsare transmitted need to be orthogonal to each other. As described abovein relation to FIG. 8, the CSI-RSs for the antenna ports may bemultiplexed using FDM, TDM and/or CDM using orthogonal frequencyresources, orthogonal time resources and/or orthogonal code resources.

When the eNB informs a UE belonging to a cell thereof of informationabout CSI-RSs, the eNB needs to signal information about time andfrequency to which a CSI-RS for each antenna port is mapped.Specifically, the information about time may include the subframenumbers of subframes in which the CSI-RS is transmitted, a CSI-RStransmission periodicity for transmission of the CSI-RS, a subframeoffset for transmission of the CSI-RS, and a number corresponding to anOFDM symbol on which a CSI-RS RE of a specific antenna is transmitted.The information about frequency may include spacing of frequencies atwhich a CSI-RS RE of a specific antenna is transmitted, and an RE offsetor a shift value in the frequency domain.

FIG. 9 is a diagram illustrating an exemplary scheme in which a CSI-RSis periodically transmitted.

The CSI-RS may be periodically transmitted with a periodicitycorresponding to an integer multiple of one subframe (e.g., 5 subframes,10 subframes, 20 subframes, 40 subframes, or 80 subframes).

FIG. 9 illustrates a case in which one radio frame consists of 10subframes (from subframe 0 to subframe 9). In the example illustrated inFIG. 9, the transmission periodicity of the CSI-RS of the eNB is 10 ms(i.e., 10 subframes), and the CSI-RS transmission offset is 3. Differentoffset values may be assigned to eNBs such that CSI-RSs of several cellsare uniformly distributed in the time domain. When the CSI-RS istransmitted with a periodicity of 10 ms, the offset may be set to avalue between 0 and 9. Similarly, when the CSI-RS is transmitted with aperiodicity of, for example, 5 ms, the offset may be set to a valuebetween 0 and 4. When the CSI-RS is transmitted with a periodicity of 20ms, the offset may be set to a value between 0 and 19. When the CSI-RSis transmitted with a periodicity of 40 ms, the offset may be set to avalue between 0 and 39. When the CSI-RS is transmitted with aperiodicity of 80 ms, the offset may be set to a value between 0 and 79.The offset value indicates the value of a subframe in which an eNBtransmitting the CSI-RS with a predetermined periodicity starts CSI-RStransmission. When the eNB informs the UE of the transmissionperiodicity and the offset value of the CSI-RS, the UE may receive theCSI-RS of the eNB at the corresponding subframe position, using thevalues. The UE may measure a channel through the received CSI-RS, andreport information such as CQI, PMI and/or rank indicator (RI) to theeNB as a result of the measurement. The CQI, the PMI and the RI may becollectively referred to as CQI (or CSI) throughout the specificationunless they are separately described. The aforementioned informationrelated to the CSI-RS is cell-specific information and may be applied tothe UEs in a cell in common. The CSI-RS transmission periodicity andoffset may be separately specified for each CSI-RS configuration. Forexample, a separate CSI-RS transmission periodicity and offset may beset for a CSI-RS configuration representing a CSI-RS transmitted withzero transmit power and a CSI-RS configuration representing a CSI-RStransmitted with non-zero transmit power.

Contrary to the CRS transmitted in all subframes in which a PDSCH can betransmitted, the CSI-RS may be configured to be transmitted only in somesubframes. For example, CSI subframe sets C_(CSI,0) and C_(CSI,1) may beconfigured by a higher layer. A CSI reference resource (i.e., apredetermined resource region forming the basis of CSI calculation) maybelong to C_(CSI,0) or C_(CSI,1), but may not belong to C_(CSI,0) andC_(CSI,1) at the same time. Accordingly, when CSI subframe setsC_(CSI,0) and C_(CSI,1) are configured by a higher layer, the UE is notallowed to expect that it will receive a trigger (or an indication forCSI calculation) for a CSI reference resource which is present in asubframe which belongs to none of the CSI subframe sets.

Alternatively, the CSI reference resource may be configured in a validdownlink subframe. The valid downlink subframe may be configured as asubframe satisfying various requirements. In the case of periodic CSIreporting, one of the requirements may be that the subframe shouldbelong to a CSI subframe set that is linked to periodic CSI reporting ifthe CSI subframe set is configured for the UE.

The UE may derive a CQI index from the CSI reference resource inconsideration of the following assumptions (For details, see 3GPP TS36.213):

-   -   First three OFDM symbols in a subframe are occupied by control        signaling        -   No REs are used by a primary synchronization signal, a            secondary synchronization signal, or a physical broadcast            channel (PBCH).    -   CP length of a non-Multicast Broadcast Single Frequency Network        (MBSFN) subframe.    -   Redundancy version is 0.    -   If a CSI-RS is used for channel measurement, the ratio of PDSCH        energy per resource element (EPRE) to CSI-RS EPRE conforms to a        predetermined rule.    -   For CSI reporting in transmission mode 9 (i.e., the mode        supporting up to S-layer transmission), if the UE is configured        for PMI/RI reporting, it is assumed that DMRS overhead        corresponds to the most recently reported rank. For example, in        the case of two or more antenna ports (i.e., rank less than or        equal to 2) as described in FIG. 7, DMRS overhead on one RB pair        is 12 REs, whereas DMRS overhead in the case of three or more        antenna ports (i.e., rank greater than or equal to 3) is 24 REs.        Therefore, a CQI index may be calculated on the assumption of        DMRS overhead corresponding to the most recently reported rank        value.    -   No REs are allocated to a CSI-RS and a zero-power CSI-RS.    -   No REs are allocated to a positioning RS (PRS).    -   The PDSCH transmission scheme conforms to a transmission mode        currently set for the UE (the mode may be a default mode).    -   The ratio of PDSCH EPRE to cell-specific RS EPRE conforms to a        predetermined rule.

The eNB may inform UEs of such a CSI-RS configuration through, forexample, radio resource control (RRC) signaling. That is, informationabout the CSI-RS configuration may be provided to UEs in a cell usingdedicated RRC signaling. For example, while a UE establishes aconnection with the eNB through initial access or handover, the eNB mayinform the UE of the CSI-RS configuration through RRC signaling.Alternatively, when the eNB transmits, to a UE, an RRC signaling messagedemanding channel state feedback based on CSI-RS measurement, the eNBmay inform the UE of the CSI-RS configuration through the RRC signalingmessage.

Meanwhile, locations of the CSI-RS in the time domain, i.e. acell-specific subframe configuration period and a cell-specific subframeoffset, may be summarized as shown in Table 1 below.

TABLE 1 CSI-RS periodicity CSI-RS subframe offset CSI-RS subframeT_(CSI-RS) Δ_(CSI-RS) configuration I_(CSI-RS) (subframes) (subframes)0-4 5 I_(CSI-RS)  5-14 10 I_(CSI-RS) - 5 15-34 20 I_(CSI-RS) - 15 35-7440 I_(CSI-RS) - 35  75-154 80 I_(CSI-RS) - 75

As described above, parameter I_(CSI-RS) may be separately configuredfor a CSI-RS assumed to have a non-zero transmit power by the UE and aCSI-RS assumed to have zero transmit power by the UE. A subframeincluding a CSI-RS may be represented by Equation 12 below (In Equation12, n_(f) is a system frame number and n_(s) is a slot number).(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS))mod T_(CSI-RS)=0  [Equation 12]

Channel State Information (CSI)

MIMO schemes may be classified into open-loop MIMO and closed-loop MIMO.

In open-loop MIMO, a MIMO transmitter performs MIMO transmission withoutreceiving CSI feedback from a MIMO receiver. In closed-loop MIMO, theMIMO transmitter receives CSI feedback from the MIMO receiver and thenperforms MIMO transmission. In closed-loop MIMO, each of the transmitterand the receiver may perform beamforming based on the CSI to achieve amultiplexing gain of MIMO Tx antennas. To allow the receiver (e.g., aUE) to feed back CSI, the transmitter (e.g., an eNB) may allocate a ULcontrol channel or a UL-SCH to the receiver.

The UE may perform estimation and/or measurement of a downlink channelusing a CRS and/or a CSI-RS. The CSI fed back to the eNB by the UE mayinclude a rank indicator (RI), a precoding matrix indicator (PMI), and achannel quality indicator (CQI).

The RI is information about a channel rank. The channel rank representsthe maximum number of layers (or streams) that can carry differentpieces of information in the same time-frequency resources. Since rankis determined mainly according to long-term fading of a channel, the RImay be fed back with a longer periodicity (namely, less frequently) thanthe PMI and the CQI.

The PMI is information about a precoding matrix used for transmissionfrom a transmitter and has a value reflecting the spatialcharacteristics of a channel. Precoding refers to mapping transmissionlayers to Tx antennas. A layer-antenna mapping relationship may bedetermined by the precoding matrix. The PMI corresponds to an index of aprecoding matrix of an eNB preferred by the UE based on a metric such assignal-to-interference-plus-noise ratio (SINR). In order to reduce thefeedback overhead of precoding information, the transmitter and thereceiver may pre-share a codebook including multiple precoding matrices,and only the index indicating a specific precoding matrix in thecodebook may be fed back. For example, the PMI may be determined basedon the most recently reported RI.

The CQI is information indicating channel quality or channel strength.The CQI may be expressed as a predetermined MCS combination. That is, aCQI index that is fed back indicates a corresponding modulation schemeand code rate. The CQI may configure a specific resource region (e.g., aregion specified by a valid subframe and/or a physical RB) as a CQIreference resource and be calculated on the assumption that PDSCHtransmission is present on the CQI reference resource, and the PDSCH canbe received without exceeding a predetermined error probability (e.g.,0.1). Generally, the CQI has a value reflecting a received SINR whichcan be obtained when the eNB configures a spatial channel using a PMI.For instance, the CQI may be calculated based on the most recentlyreported RI and/or PMI.

In a system supporting an extended antenna configuration (e.g., an LTE-Asystem), additional acquisition of multi user (MU)-MIMO diversity usingan MU-MIMO scheme is considered. In the MU-MIMO scheme, when an eNBperforms downlink transmission using CSI fed back by one UE amongmultiple users, it is necessary to prevent interference with other UEsbecause there is an interference channel between UEs multiplexed in theantenna domain. Accordingly, CSI of higher accuracy than in asingle-user (SU)-MIMO scheme should be fed back in order to correctlyperform MU-MIMO operation.

A new CSI feedback scheme may be adopted by modifying the existing CSIincluding an RI, a PMI, and a CQI so as to measure and report moreaccurate CSI. For example, precoding information fed back by thereceiver may be indicated by a combination of two PMIs (e.g., i1 andi2). Thereby, more precise PMI may be fed back, and more precise CQI maybe calculated and reported based on such precise PMI.

Meanwhile, the CSI may be periodically transmitted over a PUCCH and oraperiodically transmitted over a PUSCH. For the RI, various reportingmodes may be defined depending on which of a first PMI (e.g., W1), asecond PMI (e.g., W2), and a CQI is fed back and whether the PMI and/orCQI that is fed back relates to a wideband (WB) or a subband (SB).

CQI Calculation

Hereinafter, CQI calculation will be described in detail on theassumption that the downlink receiver is a UE. However, the descriptionof the present invention given below may also be applied to a relaystation serving to perform downlink reception.

A description will be given below of a method for configuring/defining aresource (hereinafter, referred to as a reference resource) forming thebasis of calculation of the CQI when the UE reports CSI. The CQI is morespecifically defined below.

A CQI that the UE reports corresponds to a specific index value. The CQIindex has a value indicating a modulation technique, code rate, and thelike that correspond to the channel state. For example, CQI indexes andmeanings thereof may be given as shown in Table 3 below.

TABLE 2 CQI index Modulation Code rate × 1024 Efficiency 0 out of range1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.91419 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 1 64QAM 6663.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

Based on an observation which is not restricted by time and frequency,the UE may determine the highest CQI index satisfying a predeterminedrequirement among CQI indexes 1 to 15 of Table 3 with respect to eachCQI value reported in uplink subframe n. The predetermined requirementmay be that a single PDSCH transmission block which has a combination ofa modulation scheme (e.g., MCS) and a transmission block size (TBS)corresponding to the CQI index and occupies a group of downlink physicalRBs called a CQI reference resource should be received with atransmission block error probability not exceeding 0.1 (i.e., 10%). Ifeven CQI index 1 does not satisfy the aforementioned requirement, the UEmay determine CQI index 0.

In transmission mode 9 (corresponding to transmission of up to 8 layers)and the feedback reporting mode, the UE may perform channel measurementfor calculation of the CQI value reported in uplink subframe n basedonly on the CSI-RS. In the other transmission modes and correspondingreporting modes, the UE may perform channel measurement for CQIcalculation based on the CRS.

If all requirements given below are satisfied, a combination of amodulation scheme and a TBS may correspond to one CQI index. That is,the combination should be allowed to be signaled on a PDSCH in a CQIreference resource according to an associated TRS table, the modulationscheme should be indicated by a corresponding CQI index, and when thecombination of a TBS and a modulation scheme is applied to the referenceresource, a valid channel code rate as close to the code rate indicatedby the CQI index as possible should be given. If two or morecombinations of a TBS and a modulation scheme are almost equal to thecode rate indicated by the corresponding CQI index, a combination havingthe smallest TBS may be determined.

A CQI reference resource is defined as follows.

In the frequency domain, the CQI reference resource defined as a groupof downlink physical RBs corresponds to a band associated with thederived CQI value.

In the time domain, the CQI reference resource is defined as a singledownlink subframe n-nCQI_ref. In the case of periodic CQI reporting,nCQI_ref is determined to have a value that is smallest among the valuesgreater than or equal to 4 and corresponds to a downlink subframe inwhich downlink subframe n-nCQI_ref is valid. In the case of aperiodicCQI reporting, a downlink subframe identical to a valid downlinksubframe corresponding to a CQI request in an uplink DCI format (namely,the PDCCH DCI format for providing the UE with uplink scheduling controlinformation) (or having a received CQI request) is determined as a CQIreference resource for nCQI_ref. In aperiodic CQI reporting, nCQI_refmay be 4, and downlink subframe n-nCQI_ref may correspond to a validdownlink subframe. Herein, downlink subframe n-nCQI_ref may be receivedafter a subframe corresponding to a CQI request in a random accessresponse grant (or having a received CQI request). The valid downlinksubframe refers to a downlink subframe that is configured for the UE, isnot set as a MBSFN subframe except in transmission mode 9, and neitherincludes a DwPTS field if the length of DwPTS is less than or equal to7680*Ts (Ts=1/(15000×2048) seconds), nor belongs to a measurement gapconfigured for the UE. If there is no valid downlink subframe for theCQI reference resource, CQI reporting is not performed in uplinksubframe n.

In the layer region, the CQI reference resource is defined as an RI andPMI which the CQI presumes.

The following assumptions may be made for the UE to derive a CQI indexon a CQI reference resource: (1) the first three OFDM symbols in adownlink subframe are used for control signaling; (2) there is no REthat is used by a primary synchronization signal, a secondarysynchronization signal, or a PBCH; (3) CP length of a non-MBSFN subframeis given; (4) Redundancy version is 0; (5) If a CSI-RS is used forchannel measurement, the ratio of PDSCH energy per resource element(EPRE) to CSI-RS EPRE has a predetermined value signaled by a higherlayer; (6) a PDSCH transmission scheme (single antenna porttransmission, transmit diversity, spatial multiplexing, MU-MIMO, etc.)defined for each transmission mode (e.g., a default mode) is currentlyset for the UE; (7) if the CRS is used for channel measurement, theratio of PDSCH EPRE to CRS EPRE may be determined according to apredetermined requirement. For details related to definition of the CQI,see 3GPP TS 36.213.

In summary, the downlink receiver (e.g., a UE) may configure a previousspecific single subframe as a CQI reference resource with respect to thecurrent time at which it is performing CQI calculation, and when a PDSCHis transmitted from the eNB on the CQI reference resource, may calculatea CQI value such that the error probability does not exceed 10%.

CSI Process

One or more CSI processes may be configured for a UE. Each CSI processmay be associated with a CSI-RS resource for channel measurement and aCSI-interference measurement resource (CSI-IM resource). Specifically,one CSI process is defined as an association between an NZP CSI-RSresource for measurement of a desired signal and an interferencemeasurement resource (IMR) for interference measurement. Each CSIprocess has an independent CSI feedback configuration. The independentCSI feedback configuration represents a feedback mode (the type of CSI(RI, PMI, CQI, etc.) and a transmission order of CSIs), a periodicity offeedback and a feedback offset.

One or more CSI-IM resource configurations may be provided for a UE.Higher-layer parameters such as a zero power (ZP) CSI-RS configuration(i.e., configuration information about an RE position to which a ZPCSI-RS is mapped) and a ZP CSI-RS subframe configuration (i.e.,configuration information about a periodicity and offset of occurrenceof the ZP CSI-RS) may be configured for each CSI-IM resourceconfiguration.

In addition, one or more ZP CSI-RS resource configurations may beprovided for a UE. Higher-layer parameters such as a ZP CSI-RSconfiguration list (i.e., 16-bit bitmap information about a ZP CSI-RS)and a ZP CSI-RS subframe configuration (i.e., configuration informationabout a periodicity and offset of occurrence of the ZP CSI-RS) may beconfigured for each ZP CSI-RS resource configuration.

Carrier Aggregation

Before description is given of carrier aggregation, the concept of acell introduced to manage radio resources in LTE-A will be describedfirst. A cell may be understood as a combination of downlink resourcesand uplink resources. Here, the uplink resource is not an essentialelement of the cell. Accordingly, a cell may include only downlinkresources or include downlink resources and uplink resources. Thedownlink resource may be referred to as a downlink component carrier (DLCC), and the uplink resource may be referred to as an uplink componentcarrier (UL CC). The DL CC and the UL CC may be represented by carrierfrequencies, and a carrier frequency represents a center frequencywithin the corresponding cell.

Cells may be divided into a primary cell (PCell), which operates at aprimary frequency, and a secondary cell (SCell), which operates at asecondary frequency. The PCell and the SCell may be collectivelyreferred to as a serving cell. A cell designated when the UE performs aninitial connection establishment procedure or during a connectionre-establishment procedure or a handover procedure, may serve as thePCell. In other words, the PCell may be understood as a cell that servesas a control-related center in a carrier aggregation environment, whichwill be described in detail later. A UE may be assigned a PUCCH in thePCell thereof and may then transmit the assigned PUCCH. The SCell may beconfigured after establishment of radio resource control (RRC)connection, and SCell may be used for providing additional radioresources. In the carrier aggregation environment, all serving cellsexcept the PCell may be viewed as SCells. In the case in which a UE isin an RRC_CONNECTED state but carrier aggregation is not established orin a case in which the UE does not support carrier aggregation, only asingle serving cell consisting of PCells exists. On the other hand, inthe case in which a UE is in the RRC_CONNECTED state and carrieraggregation is established therefor, one or more serving cells exist,and PCells and all SCells are included in all serving cells. For a UEsupporting carrier aggregation, after an initial security activationprocedure is initiated, the network may configure one or more SCells inaddition to a PCell configured at the beginning of the connectionestablishment procedure.

Carrier aggregation is a technology that has been introduced to allowfor use of a broader band in order to meet the requirements of ahigh-speed transmission rate. Carrier aggregation may be defined asaggregation of two or more component carriers (CCs) having differentcarrier frequencies or aggregation of two or more cells. Herein, CCs maybe consecutive or non-consecutive in the frequency domain

The UE may simultaneously receive and monitor downlink data from aplurality of DL CCs. A linkage between a DL CC and a UL CC may beindicated by the system information. The DL CC/UL CC link may be fixedin the system or may be semi-statically configured. Additionally, evenif the entire system band consists of N CCs, the frequency band in whicha specific UE can perform monitoring/reception may be limited to M(<N)CCs. Various parameters for carrier aggregation may be set up in acell-specific, UE group-specific, or UE-specific manner.

Cross-carrier scheduling refers to, for example, including all downlinkscheduling allocation information about a DL CC in the control region ofanother DL CC for one of multiple serving cells or including all ULscheduling grant information about multiple UL CCs linked to a DL CC forone of multiple serving cells in the control region of the DL CC.

Regarding cross-carrier scheduling, a carrier indicator field (CIF) willbe described first. The CIF may be included in the DCI formattransmitted over the PDCCH (and be defined to have, for example, a sizeof 3 bits), or may not be included in the DCI format (in this case, theCIF may be defined to have, for example, a size of 0 bits). If the CIFis included in the DCI format, this indicates that cross-carrierscheduling is applied. In the case in which cross-carrier scheduling isnot applied, the downlink scheduling allocation information is validwithin the DL CC through which downlink scheduling allocationinformation is currently being transmitted. Additionally, the uplinkscheduling grant is valid for a UL CC linked to the DL CC through whichthe downlink scheduling allocation information is transmitted.

In the case in which cross-carrier scheduling is applied, the CIFindicates a CC related to the downlink scheduling allocation informationwhich is transmitted over the PDCCH in a DL CC. For example, downlinkallocation information about DL CC B and DL CC C, i.e., informationabout PDSCH resources, is transmitted over the PDCCH within the controlregion of DL CC A. The UE may monitor DL CC A so as to recognize theresource region of the PDSCH and the corresponding CC through the CIF.

Whether or not the CIF is included in the PDCCH may be semi-staticallyset, and the CIF may be UE-specifically enabled by higher-layersignaling.

When the CIF is disabled, the PDCCH in a specific DL CC allocates aPDSCH resource in the same DL CC and may also allocate a PUSCH resourcein a UL CC linked to the specific DL CC. In this case, the same codingscheme, CCE-based resource mapping and DCI format as used in the legacyPDCCH structure may be applied.

When the CIF is enabled, the PDCCH in a specific DL CC may allocate aPDSCH/PUSCH resource within a single DL/UL CC indicated by the CIF,among the multiple aggregated CCs. In this case, a CIF may beadditionally defined in the legacy PDCCH DCI format. The CIF may bedefined as a field having a fixed length of 3 bits, or the CIF positionmay be fixed regardless of the size of the DCI format. The codingscheme, CCE-based resource mapping, DCI format, and so on of the legacyPDCCH structure may be applied to this case.

When the CIF exists, an eNB may allocate a DL CC set in which the PDCCHis to be monitored. Accordingly, UE burden of blind decoding may belessened. The PDCCH monitoring CC set corresponds to a portion of allaggregated DL CCs, and the UE may perform PDCCH detection/decoding onlyin the corresponding CC set. In other words, in order to performPDSCH/PUSCH scheduling for a UE, the eNB may transmit the PDCCH only inthe PDCCH monitoring CC set. The PDCCH monitoring CC set may beUE-specifically, UE group-specifically or cell-specifically configured.For example, when 3 DL CCs are aggregated, DL CC A may be configured asa PDCCH monitoring DL CC. If the CIF is disabled, the PDCCH in each DLCC may schedule only the PDSCH within the DL CC A. On the other hand, ifthe CIF is enabled, the PDCCH in DL CC A may schedule not only the PDCCHof the DL CC A but also the PDSCH of the other DL CCs. In the case wherethe DL CC A is configured as the PDCCH monitoring CC, the PDCCH may notbe transmitted in DL CC B and DL CC C.

Quasi Co-Location (QCL)

A QC or QCL (Quasi Co-Located) relationship can be explained in terms ofa signal or channel.

When large-scale properties of a signal received through one antennaport can be inferred from another signal received through anotherantenna port, the two antenna ports may be said to be QCL. Herein, thelarge-scale properties may include at least one of a delay spread, aDoppler shift, a frequency shift, an average received power, andreceived timing.

Alternatively, two antenna ports may be said to be QCL when large-scaleproperties of a channel over which a symbol on one antenna port istransmitted can be inferred from properties of a channel over whichanother symbol on the other antenna port is transmitted. Herein, thelarge-scale properties may include at least one of a delay spread, aDoppler spread, a Doppler shift, an average gain, and an average delay.

In this disclosure, definition of the term QC or QCL is notdistinguished among the signals or channels described above.

The UE may assume that any two antenna ports having the QCL assumptionestablished therebetween are co-located even if the antenna ports arenot actually co-located. For example, the UE may assume that two antennaports having the QCL assumption established therebetween are at the sametransmission point (TP).

For example, a specific CSI-RS antenna port, a specific downlink DMRSantenna port, and a specific CRS antenna port may be configured to beQCL. This configuration may correspond to a case in which the specificCSI-RS antenna port, the specific downlink DMRS antenna port, and thespecific CRS antenna port are from one serving cell.

Alternatively, a CSI-RS antenna port and a downlink DMRS antenna portmay be configured to be QCL. For example, in a CoMP environment in whicha plurality of TPs participates, a TP from which a CSI-RS antenna portis actually transmitted may not be explicitly known to the UE. In thiscase, the UE may be informed that a specific CSI-RS antenna port and aspecific DMRS antenna port are QCL. This may correspond to a case inwhich the specific CSI-RS antenna port and the specific DMRS antennaport are from a certain TP.

In this case, the UE may increase the performance of channel estimationthrough a DMRS, based on the information about large-scale properties ofa channel acquired using a CSI-RS or a CRS. For example, the UE mayperform an operation of, for example, attenuating interference of achannel estimated through the DMRS, using the delay spread of a channelestimated through the CSI-RS.

For example, regarding delay spread and Doppler spread, the UE may applyestimation results of the power-delay-profile, the delay spread andDoppler spectrum and the Doppler spread for one antenna port to a Wienerfilter which is used in performing channel estimation for anotherantenna port. In addition, regarding frequency shift and receivedtiming, after the UE performs time and frequency synchronization for anantenna port, it may apply the same synchronization to demodulation onanother antenna port. Further, regarding average received power, the UEmay average measurements of reference signal received power (RSRP) overtwo or more antenna ports.

For example, the UE may receive DL scheduling information through aspecific DMRS-based DL-related DCI format over a PDCCH or anenhanced-PDCCH (EPDCCH). In this case, the UE performs channelestimation of a scheduled PDSCH through a configured DMRS sequence andthen performs data demodulation. For example, if the UE can make a QCLassumption that a DMRS port configuration received from the DLscheduling information and a port for a specific RS (e.g., a specificCSI-RS, a specific CRS, a DL serving cell CRS of the UE, etc.) are QCL,then the UE may apply the estimates of the large-scale properties suchas the delay spread estimated through the port for the specific RS toimplementation of channel estimation through the DMRS port, therebyimproving performance of DMRS-based reception.

This is because the CSI-RS or CRS is a cell-specific signal transmittedover the full band in the frequency domain, and thus allows for moreaccurate recognition of large-scale properties of a channel than theDMRS. Particularly, the CRS is a reference signal that is broadcast witha relatively high density over the full band in every subframe asdescribed above, and thus, generally, estimates of the large-scaleproperties of a channel may be more stably and accurately acquired fromthe CRS. On the other hand, the DMRS is UE-specifically transmitted onlyon specific scheduled RBs, and accordingly accuracy of estimates of thelarge-scale properties of a channel is lower than in the case of the CRSor the CSI-RS. In addition, even if a plurality of physical resourceblock groups (PBRGs) is scheduled for a UE, an effective channelreceived by the UE may change on a PRBG-by-PRBG basis since a precodingmatrix that the eNB uses for transmission may change on the PRBG-by-PRBGbasis. Thereby, the accuracy of estimation may be lowered even iflarge-scale properties of a radio channel are estimated based on theDMRS over a wide band.

For antenna ports (APs) which are not QCL (non-quasi-co-located (NQC)),the UE cannot assume that the APs have the same large-scale properties.In this case, the UE needs to perform independent processing for eachNQC AP regarding timing acquisition and tracking, frequency offsetestimation and compensation, delay estimation, and Doppler estimation.

PDSCH Resource Mapping Parameters

Information indicating whether or not APs are QCL may be provided to theUE through DL control information (e.g., a PQI field of DCI format 2D (aPDSCH RE mapping and QCL indicator field)). Specifically, parameter sets(e.g., a maximum of four parameter sets) for a QCL configuration may bepreconfigured by a higher layer, and a specific one of the QCL parametersets may be indicated through the PQI field of DCI format 2D.

In addition, to decode a PDSCH transmitted on APs #7 to #14 (i.e.,UE-specific RS APs), at least one of QCL type A and type B may beconfigured for the UE by a higher layer (according to, for example,higher layer parameter qcl-operation).

QCL type A may be an operation of the UE assuming that APs #0 to #3(i.e., CRS APs), #7 to #14 (i.e., UE-specific RS APs) and #15 to #22(i.e., CSI-RS AP) are QCL with respect to delay spread, Doppler spread,Doppler shift and average delay.

QCL type B may be an operation of the UE assuming that APs #15 to #22(i.e., CSI-RS APs) corresponding to CSI-RS resource configurationsidentified by non-zero power (NZP) CSI-RS configuration information(qcl-CSI-RS-ConfigNZPId-r11) given by a higher layer and APs #7 to #14(i.e., UE-specific RS APs) associated with PDSCH are QCL with respect todelay spread, Doppler spread, Doppler shift and average delay.

A UE set to QCL type B may determine PDSCH RE mapping using a parameterset indicate by the PQI field of DCI format 2D of the detectedPDCCH/EPDCCH and also determine PDSCH AP QCL. Table 3 below shows thePQI field of DCI format 2D.

TABLE 3 Value of the PQI field Description ‘00’ Parameter set 1configured by a higher layer ‘01’ Parameter set 2 configured by a higherlayer ‘10’ Parameter set 3 configured by a higher layer ‘11’ Parameterset 4 configured by a higher layer

Each parameter set for determining PDSCH RE mapping and PDSCH AP QCLconfigured by higher layer signaling may include at least one parameterof CRS port count information (crs-PortsCount-r11), CRS frequency shiftinformation (crs-FreqShift-r11), MBSFN (Multicast Broadcast SingleFrequency Network) subframe configuration information(mbsfn-SubframeConfigList-r11), ZP CSI-RS (Zero Power Channel StateInformation-Reference Signal) configuration information(csi-RS-ConfigZPId-r11), a PDSCH start symbol value (pdsch-Start-r11)and NZP (Non-Zero Power) CSI-RS configuration information(qcl-CSI-RS-ConfigNZPId-r11).

The UE set to QCL type B may decode PDSCH transmitted through AP #7using parameter set 1 of Table 3, by which the UE detects a PDCCH/EPDCCHof DCI format 1A CRC-masked with C-RNTI.

In decoding the PDSCH scheduled according to PDCCH/EPDCCH of DCI format1A, if the PDSCH is transmitted through APs #0 to #3 (i.e., CRS APs),the UE may determine PDSCH RE mapping using a ZP CSI-RS resource havingthe lowest index.

Antenna Port QCL for PDSCH

A UE may assume that APs #0 to #3 (i.e., CRS APs) of the serving cellare QCL with respect to delay spread, Doppler spread, Doppler shift,average gain and average delay.

The UE may assume that APs #7 to #14 (i.e., UE-specific RS APs) of theserving cell are QCL with respect to delay spread, Doppler spread,Doppler shift, average gain and average delay.

The UE may assume that APs #0 to #3 (i.e., CRS APs), #5 (i.e.,UE-Specific RS APs defined in 3GPP LTE Release 8), #7 to #14 (i.e.,UE-Specific RS APs defined after 3GPP LTE Release 9) and #15 to #22(i.e., CSI-RS APs) are QCL with respect to Doppler shift, Dopplerspread, average delay and average spread.

Definition of CSI-RS in Consideration of QCL

In addition to the description of CSI-RS configurations given above,definition of a CSI-RS in consideration of QCL is described below.

One or more CSI-RS resource configurations may be provided for a UE by ahigher layer. The CSI-RS resource configuration may include at least oneof CSI-RS resource configuration identification information, the numberof CSI-RS ports, a CSI-RS configuration (i.e., configuration for an REposition to which a CSI-RS is mapped), a CSI-RS subframe configuration,a UE assumption about transmit power of a reference PDSCH for each CSIprocess, a pseudo-random sequence generator parameter, and a higherlayer parameter (gel-CRS-Info-r11) for an assumption on CRS APs andCSI-RS APs for QCL type B. Herein, the parameter gel-CRS-Info-r11 mayinclude a pseudo-random sequence generator parameter(qcl-ScramblingIdentity-r11), a CRS port count parameter(crs-PortsCount-r11) and an MBSFN subframe configuration information(mbsfn-SubframeConfigList-r11).

The UE may assume that CSI-RS APs for one CSI-RS resource configurationare QCL with respect to average spread, Doppler spread, Doppler shift,average gain and average delay.

A UE set to QCL type B may assume that CRS APs #0 to #3 related to thegel-CRS-Info-r11 parameter corresponding to a CSI-RS resourceconfiguration and CSI-RS APs #15 to #22 corresponding to the CSI-RSresource configuration are QCL with respect to Doppler shift and Dopplerspread.

Coordinated Multi-Point (CoMP)

To satisfy requirements for enhanced system performance of the 3GPPLTE-A system, CoMP transmission and reception technology (also calledco-MIMO, collaborative MIMO or network MIMO) has been proposed. CoMPtechnology may increase the performance of UEs located at a cell edgeand the average sector throughput.

In a multi-cell environment with a frequency reuse factor of 1, theperformance of a UE located at a cell edge and the average sectorthroughput may be lowered due to inter-cell interference (ICI). Toattenuate ICI, the legacy LTE system has adopted a simple passivetechnique such as fractional frequency reuse (FFR) based on UE-specificpower control such that a UE located at a cell edge may have appropriatethroughput in an environment constrained by interference. However,attenuating the ICI or reusing ICI as a desired signal for the UE may bemore preferable than lowering use of frequency resources per cell. Tothis end, a CoMP transmission technique may be employed.

CoMP schemes applicable to downlink may be broadly classified into jointprocessing (JP) and coordinated scheduling/beamforming (CS/CB).

According to the JP scheme, data can be used by each point (eNB) of aCoMP cooperation unit. The CoMP cooperation unit refers to a set of eNBsused for a CoMP transmission scheme. The JP scheme may be furtherdivided into joint transmission and dynamic cell selection.

Joint transmission refers to a technique of simultaneously transmittingPDSCHs from a plurality of points (a part or the entirety of a CoMPcooperation unit). That is, a plurality of points may simultaneouslytransmit data to a single UE. With the joint transmission scheme, thequality of a received signal may be coherently or non-coherentlyimproved, and interference with other UEs may be actively eliminated.

Dynamic cell selection is a technique of transmitting a PDSCH from onepoint (of a CoMP cooperation unit) at a time. That is, one pointtransmits data to a single UE at a given time, while the other points inthe CoMP cooperation unit do not transmit data to the UE at the giventime. A point to transmit data to a UE may be dynamically selected.

Meanwhile, in the CS/CB scheme, CoMP cooperation units may cooperativelyperform beamforming for data transmission to a single UE. Herein, userscheduling/beamforming may be determined through coordination amongcells of a CoMP cooperation unit, whereas data is transmitted to the UEonly from a serving cell.

In the case of uplink, CoMP reception refers to reception of a signaltransmitted through cooperation among a plurality of geographicallyseparated points. The CoMP schemes applicable to uplink may beclassified into joint reception (JR) and coordinatedscheduling/coordinated beamforming (CS/CB).

The JR scheme indicates that a plurality of reception points receives asignal transmitted through a PUSCH. The CS/CB scheme indicates that aPUSCH is received by only one point, but user scheduling/beamforming isdetermined by coordination among the cells of a CoMP unit.

With the CoMP system as above, multi-cell base stations may jointlysupport data for a UE. In addition, the base stations may simultaneouslysupport one or more UEs using the same radio frequency resources,thereby increasing system performance. Moreover, a base station mayperform space division multiple access (SDMA) based on CSI between theUE and the base station.

In the CoMP system, a serving eNB and one or more cooperative eNBs areconnected to a scheduler over a backbone network. The scheduler mayreceive channel information about the channel states between each UE andcooperative eNBs measured and fed back by the cooperative eNBs over thebackbone network, and operate based on the channel information. Forexample, the scheduler may schedule information for a cooperative MIMOoperation for the serving eNB and the one or more cooperative eNBs. Thatis, the scheduler may directly issue a command about the cooperativeMIMO operation to each eNB.

As described above, the CoMP system may be expected to operate as avirtual MIMO system by grouping a plurality of cells into one group.Basically, the CoMP system may adopt a MIMO communication schemeemploying multiple antennas.

CoMP and CSI Process

FIG. 10 illustrates an exemplary downlink CoMP operation.

In FIG. 10, a UE is positioned between eNB1 and eNB2 and the two eNBs,i.e. eNB1 and eNB2, perform a proper CoMP operation such as jointtransmission (JT), dynamic cell selection (DCS), or CS/CB to solve aproblem of interference to the UE. To aid in the CoMP operation of theeNBs, the UE performs proper CSI feedback. Information transmittedthrough CSI feedback includes RI, PMI and CQI of each eNB and mayadditionally include channel information between the two eNBs (e.g.phase offset information between a channel from eNB1 to the UE and achannel from eNB2 to the UE) for JT.

While FIG. 10 illustrates the UE as transmitting a CSI feedback signalto eNB1 which is the serving cell thereof, the UE may transmit the CSIfeedback signal to the eNB2 or to both eNBs depending on the situation.

That is, to support CoMP scheduling in a network, the UE may feed backnot only downlink (DL) CSI of a serving eNB/TP but also DL CSI of aneighboring eNB/TP. To this end, the UE may generate and feed back CSIabout a plurality of CSI processes reflecting various interferenceenvironments of eNBs/TPs for data transmission.

An interference measurement resource (IMR) is used to measureinterference when CoMP CSI calculation is performed. One or more IMRsmay be configured for a UE. Each IMR may be independently configured.That is, a period, subframe offset, and resource configuration (i.e., REmapping location) may be independently set for each IMR, and informationthereabout may be signaled from the network to the UE via a higher layer(e.g., an RRC layer).

A CSI-RS is used to measure a desired channel or signal for CoMP CSIcalculation. One or more CSI-RSs may be configured for a UE. Each of theCSI-RSs is independently configured. That is, a transmission period,subframe offset, resource configuration (i.e., RE mapping location),assumption on transmit power (i.e., parameter Pc), and the number of APsmay be independently configured for each CSI-RS and signaled from thenetwork to the UE via a higher layer (e.g., an RRC layer).

One CSI process is defined by an association (combination) between oneCSI-RS resource for signal measurement and one IMR for interferencemeasurement from among the CSI-RSs and IMRs configured for the UE. TheUE may feed back, to the network, CSI calculated or derived fromdifferent CSI processes according to the independent periods andsubframe offsets. That is, each CSI process may have an independent CSIfeedback configuration. The network may provide the UE with theinformation about the association (or combination) between a CSI-RSresource and an IMR and CSI feedback configuration through higher layersignaling (e.g. RRC signaling, etc.) according to each CSI process. Forexample, in FIG. 10, three CSI processes as shown in Table 4 may beconfigured for the UE.

TABLE 4 CSI process SMR IMR CSI process 0 CSI-RS 0 IMR 0 CSI process 1CSI-RS 1 IMR 1 CSI process 2 CSI-RS 0 IMR 2

In Table 4, CSI-RS 0 and CSI-RS 1 respectively represent a CSI-RSreceived from eNB1 which is a serving eNB of the UE and a CSI-RSreceived from eNB2 which is a neighboring eNB participating incooperation.

Table 5 below shows configurations of the three IMRs of Table 4. IMR 0is set as a resource on which eNB1 performs muting (or transmission of anull signal), and eNB2 performs data transmission. The UE measuresinterference from eNBs except for eNB1 on IMR 0. IMR 1 is set as aresource on which eNB2 performs muting, and eNB1 performs datatransmission. The UE measures interference from the eNBs except for eNB2based on IMR 1. IMR 2 is set as a resource on which both eNB1 and eNB2perform muting. The UE measures interference from eNBs except for eNB1and eNB2 based on IMR 2.

TABLE 5 IMR eNB1 eNB2 IMR 0 muting data transmission IMR 1 datatransmission muting IMR 2 muting muting

In Table 4, CSI of CSI process 0 indicates optimum RI, PMI, and CQIgiven when data is received from eNB1. CSI of CSI process 1 indicatesoptimum RI, PMI, and CQI given when data is received from eNB2. CSI ofCSI process 2 indicates optimum RI, PMI, and CQI given when data isreceived from eNB1 and there is no interference from eNB2.

Improvement of NIB CoMP

A non-ideal backhaul (NIB) network refers to a network that has acertain delay (of, for example, 5 to 30 ms) in signal transmission andreception on a backhaul link between geographically separated CoMPpoints. The legacy CoMP operation has been designed on the assumption ofan ideal situation in which control information is communicated on abackhaul link between CoMP points without suffering a delay, and thusenables dynamic scheduling decision between CoMP points on asubframe-by-subframe basis. For example, a dynamic point switching (DPS)scheme in which a TP for transmitting PDSCH is changed in every subframemay be supported. For example, DL assignment of DCI format 2D isprovided to the UE which is set to transmission mode10 (TM10) to supportDPS, the 2-bit PQI field in DCI format 2D may be indicated by a specificstatus value. Thereby, PDSCH RE mapping information about a TPtransmitting PDSCH and QCL information between RSs may be dynamicallyprovided.

However, the legacy CoMP operation cannot be applied to a CoMP operationon the NIB network. For example, if a backhaul link between pointsparticipating in CoMP is an NIB, the PDSCH scheduling should bepredetermined and shared between two points prior to delay intransmission and reception on the NIB in order for one point to informof scheduling information about a PDSCH transmitted from the other pointin a current subframe by providing the UE with DCI format 2D containinga PQI field in the subframe. This operation is close to static PDSCHscheduling according to a predetermined pattern rather than dynamicpoint selection. Accordingly, it is difficult to support the legacy CoMPoperation on the NIB.

In this regard, the present invention proposes a method for correctlyand efficiently performing or supporting CoMP on an NIB network

Description given below mainly focuses on CoMP operation between eNBs,but the principle of the present invention may also be applied to CoMPoperation between a TP, RP, remote radio head (RRH), and relay. That is,any of the terms eNB, TP, RP, RRH and relay encompasses all of the otherterms.

Hereinafter, the present invention will be described based on a 3GPP LTEsystem, but the principle of the present invention is also applicable toa communication system based on another technology.

Xn-Signaling Information for NIB CoMP

FIG. 11 illustrates a situation in which CoMP is not applied.

In FIG. 11, TP1 is the serving cell of the UE, and the UE receives DLscheduling information. The UE also receives a PDSCH from TP1.

In non-CoMP as shown in FIG. 11, TP1 and TP2 may exchange signaling forcooperative transmission through an NIB link. Since signaling forcooperative transmission is transmitted on an Xn link (e.g., X2link/backhaul link) referring to a link between TPs, it may have theform of Xn-signaling. In addition, the signaling for cooperativetransmission may include at least one of loading information,information about one or more CSI-RS configurations, information aboutone or more CSI-IM (or IMR) configurations and DMRS configurationinformation.

The loading information (or congestion information) may includeinformation about the number of UEs accessing a specific TP (i.e., UEsconsidering the TP as the serving cell thereof). Additionally oralternatively, the loading information may include informationindicating a portion in use or a surplus portion of the serviceablecapacity of the specific TP such as, for example, a ratio (percentage)of the number of UEs currently accessing the specific TP to the maximumnumber of UEs capable of accessing the specific TP. The specific TP maydeliver such loading information to another TP through Xn-signaling ormulticast/broadcast the same to a plurality of TPs. In addition, thespecific TP may make a request for provision of such loading informationto other TPs.

The information about one or more CSI-RS configurations may include NZPCSI-RS configuration information (e.g., NZP CSI-RS RE location, period,offset, etc.) about a specific TP and/or ZP CSI-RS configurationinformation (e.g., ZP CSI-RS RE location, period, offset, etc.) aboutthe specific TP. The NZP CSI-RS configuration information may be relatedto one or more NZP CSI-RS configurations, an NZP CSI-RS which the TP isactually transmitting, or an NZP CSI-RS configured for a specific UE.The ZP CSI-RS configuration information may be related to one or more ZPCSI-RS configurations and be applied to PDSCH rate matching. A specificTP may deliver the information about one or more CSI-RS configurationsto another TP through Xn-signaling, or multicast/broadcast the same to aplurality of TPs. In addition, the specific TP may make a request forprovision of information about one or more CSI-RS configurations toother TPs.

The information about one or more CSI-IM (or IMR) configurations mayinclude information about one or more CSI-IM configurations (e.g., ZPCSI-RS RE location, period, offset, etc.) of a specific TP and/orinformation about whether or not the specific TP performs muting (ortransmission) with respect to each of the CSI-IM configurations at thecorresponding RE location. The information about the CSI-RSconfigurations of the specific TP may include information about a CSI-IMconfiguration established for specific UEs by the specific TP andinformation about a CSI-IM configuration (e.g., ZP CSI-RS RE location,period, offset, etc.) which is not established for UEs associated withthe specific TP but established for UEs of neighboring TPs to provide aspecific interference environment in which the UEs calculate/generateCSI. The specific TP may deliver such information about one or moreCSI-IM configurations to another TP through Xn-signaling ormulticast/broadcast the same to a plurality of TPs. In addition, thespecific TP may make a request to other TPs for provision of theinformation about one or more CSI-IM configurations. The specific TP mayalso make a request to other TPs for performing muting (or transmission)at an RE location of a specific CSI-IM configuration.

For the DMRS configuration information, there is a need to supportXn-signaling for pre-exchanging, between TPs, a DMRS configuration(e.g., DMRS sequence scrambling initialization parameters) to be appliedif a TP transmits a PDSCH to each of UEs which are targets of CoMPtransmission. For example, in a CoMP situation in which TP1 and TP2 areswitched at different time intervals to transmit a PDSCH for the UE, TP2needs to preannounce to TP1, through Xn-signaling, DMRS configurationinformation which TP2 uses to transmit a PDSCH to the UE. The UE cancorrectly perform PDSCH reception only when TP1 announces the DMRSconfiguration information to the UE through RRC signaling. This isbecause the latency of RRC signaling from TP1 to the UE may be greaterthan that of Xn-signaling between TP1 and TP2. Accordingly, if TP1announces the DMRS configuration information pre-received from TP2 tothe UE through RRC signaling, the UE may correctly receive the PDSCHfrom TP2 based on the DMRS configuration of TP2.

Herein, information about a specific CSI-IM configuration needs to beuniquely indicated within a network (e.g., a CoMP cluster) including aplurality of TPs. That is, for TP2 having received informationindicating a specific CSI-IM configuration intended by TP1 to know theCSI-IM configuration intended by TP1 from the information, CSI-IMconfiguration information indicating a corresponding CSI-IMconfiguration needs to be predefined among the TPs. Accordingly, thepresent invention proposes that network-wise CSI-IM configurationinformation (hereinafter, NW-CSI-IM configuration information) bedefined. For example, NW-CSI-IM configuration information may be definedby an NW-CSI-IM index (or NW-CSI-IM configuration index) to each CSI-IMconfiguration. The NW-CSI-IM configuration information may becommunicated between TPs in the form of Xn-signaling.

For example, suppose that three eNBs construct one CoMP cluster. In thiscase, M NW-CSI-IM indexes may be defined. For example, 7 NW-CSI-IMindexes may be given as shown in Table 6 below.

TABLE 6 NW-CSI-IM index eNB1 eNB2 eNB3 NW-CSI-IM index 1 Muting mutingmuting NW-CSI-IM index 2 Muting muting non-muting NW-CSI-IM index 3Muting non-muting muting NW-CSI-IM index 4 Muting non-muting non-mutingNW-CSI-IM index 5 non-muting muting muting NW-CSI-IM index 6 non-mutingmuting non-muting NW-CSI-IM index 7 non-muting non-muting muting

As shown in Table 6, the proposed NW-CSI-IM configuration informationmay directly indicate whether or not muting is to be performed for eachspecific eNB.

Table 6 is simply illustrative. Event cases marked by “non-muting” maybe subdivided into a plurality of transmit power levels. In this case, Mmay be set to a value greater than 7. When NW-CSI-IM configurationinformation is defined in consideration of various interferencehypotheses as above, M may be set to a value greater than 7.Alternatively, if only some cases are defined without considering allcases of muting of each eNB, M may be set to a value less than 7.

The NW-CSI-IM configuration information may not only indicate muting ofeach eNB (or a power level for non-muting) but also indicate that thebehavior of a specific eNB does not matter. For example, the NW-CSI-IMconfiguration information may be defined as indicating “muting,”“non-muting,” or “don't care” for each eNB in the CoMP cluster. Forexample, NW-CSI-IM index 8 may be added to Table 6. Thereby, theNW-CSI-IM configuration information may be defined as shown in Table 7below.

TABLE 7 NW-CSI-IM index eNB1 eNB2 eNB3 NW-CSI-IM index 1 muting mutingmuting NW-CSI-IM index 2 muting muting non-muting NW-CSI-IM index 3muting non-muting muting NW-CSI-IM index 4 muting non-muting non-mutingNW-CSI-IM index 5 non-muting muting Muting NW-CSI-IM index 6 non-mutingmuting non-muting NW-CSI-IM index 7 non-muting non-muting MutingNW-CSI-IM index 8 non-muting don't care Muting

That is, in NW-CSI-IM index 8, the operation of eNB2 on thecorresponding NW-CSI-IM resource may be set to “don't care”. This meansthat eNB2 may determine, as eNB2 desires, whether to perform muting ornon-muting on the corresponding NW-CSI-IM resource or precoding andpower assignment applied to a signal to be transmitted when eNB2performs non-muting. Accordingly, the other eNBs (e.g., eNB1 and eNB3)cannot predict the behavior that eNB2 performs on the correspondingNW-CSI-IM resource, it may not be ensured that interference caused byeNB2 is uniform.

As in the examples above, an Xn-signaling format (e.g., backhaulsignaling format) explicitly indicating hypotheses of behaviors ofindividual eNBs on a specific CSI-IM resource may be designed, andCSI-IM configuration information may be exchanged between eNBs accordingto the Xn-signaling format. For example, each NW-CSI-IM index may bedefined as explicitly indicating, for each eNB, one or more elementsfrom a set including {muting, a predetermined maximum or minimum powerlevel value, specific precoding information (e.g., a beam direction, aprecoding coefficient, or a precoding set), “don't care”}, and backhaulsignaling may be performed using a specific NW-CSI-IM index.

In addition, the NW-CSI-IM configuration information may be used insignaling between eNBs, or may be used as information about a CoMPhypothesis indicated to the UE by an eNB. For example, eNB1 mayconfigure some (or all) of the NW-CSI-IM indexes 1, 2, 3 and 4 for UEsaccessing eNB1 through a higher layer signal such as an RRC signal. Forexample, two NW-CSI-IM indexes of NW-CSI-IM index 4 (reflecting anon-CoMP interference environment) and NW-CSI-IM index 2 (reflecting aCoMP environment in which eNB2 performs muting) may be configured,through an RRC signal, for CoMP UE1 accessing eNB1, and NW-CSI-IMindexes 2 and 4 may be included in a separate CSI process. Thereby, CoMPUE1 may calculate/generate CSI based on different CoMP hypotheses (e.g.,different interference environments) and feed the same back to eNB1. Forexample, for CoMP UE1, NW-CSI-IM index 4 may be configured ascsi-IM-ConfigId-r11=1, and NW-CSI-IM index 2 may be configured ascsi-IM-ConfigId-r11=2.

That is, one of {1, . . . , maxCSI-IM-r11} may be designated and set asa csi-IM-ConfigId-r11 value for individual UEs, and may correspond tothe NW-CSI-IM index 1, . . . , 7 uniquely assigned on a network (e.g., aCoMP cluster).

As another example, eNB2 may configure some (or all) of NW-CSI-IMindexes 1, 2, 5 and 6 for UEs accessing eNB2 through a higher layersignal such as an RRC signal, and the UEs may calculate and feed backCSI in consideration of different CoMP environments corresponding to theNW-CSI-IM indexes.

In the examples above, methods to define information indicating a CSI-IMconfiguration network-wise have been mainly described. The sameprinciple may also be applied to NZP CSI-RS configuration informationand ZP CSI-RS configuration information. That is, by definingNW-NZP-CSI-RS configuration information (or an NW-NZP-CSI-RS index)and/or NW-ZP-CSI-RS configuration information (or an NW-ZP-CSI-RS index)in a specific-scale network (e.g., CoMP cluster) including a pluralityof eNBs, a specific NW-NZP-CSI-RS configuration and/or specificNW-ZP-CSI-RS configuration may be uniquely designated for the eNBs (andUEs served by the eNBs) in the network.

Further, the concept of network-wise definition of informationindicating a CSI-IM configuration may also be applied to CSI processconfiguration information. For example, one CSI process index may bedefined as a combination of (one) NZP CSI-RS index and (one) CSI-IMindex. That is, by defining NW-CSI-process configuration information (oran NW-CSI-process index) in a specific-scale network (e.g., a CoMPcluster) including a plurality of eNBs, a specific NW-CSI-processconfiguration may be uniquely designated for eNBs (and UEs served by theeNBs) in the network.

The aforementioned loading information, information about one or moreCSI-RS configurations, information about one or more CSI-IM (or IMR)configurations, or DMRS configuration information may need to bepre-exchanged (or periodically exchanged) between TPs participating in aCoMP operation through, for example, Xn-signaling. That is, suchinformation may need to be pre-exchanged between TPs participating inthe NIB CoMP operation through, for example, Xn-signaling in order touse the information to determine when to initiate the CoMP operation(e.g., TP1 performs muting in a situation of loading of TP1 if possible)even if there is an Xn-signaling delay (of, for example, tens ofmilliseconds).

The loading information, information about one or more CSI-RSconfigurations, information about one or more CSI-IM (or IMR)configurations, or DMRS configuration information may not be limited touse during CoMP operation, but may also be used for other purposes, forexample, to support the operation of a UE employing a network-assistedinterference cancellation and suppression scheme.

Xn-Signaling for SSPM

FIG. 12 illustrates an SSPM technique.

As a technique to use Xn-signaling between TPs to allow for NIB CoMPoperation, semi-static point muting (SSPM) may be employed. Hereinafter,additional features of Xn-signaling which are considered for SSPM willbe described.

SSPM is a scheme in which only a specific TP (e.g., serving TP1)transmits a PDSCH, and neighboring TPs performs muting in apredetermined band in a predetermined time interval. Information aboutthe time interval and band in which the TPs perform muting may bepre-agreed between the TPs through Xn-signaling. According to the SSPMscheme in which neighboring TPs do not perform transmission in aspecific band in a specific time interval, interference applied by theneighboring TPs may be minimized, and accordingly performance ofreceiving a PDSCH from a serving TP may be maximized in view of a CoMPUE.

1-Way Xn-Signaling for Initiation of SSPM

Xn-signaling for SSPM may be defined as being broadcast (unicast ormulticast to one or more other TPs) by a specific TP in a 1-way manner.

The information provided by the TP transmitting the Xn-signaling may bea message for informing (promising) that the TP or other TPs willperform muting in a “specific band” in a “specific time interval”.

Herein, the “specific time interval” may have a value expressed in apredetermined time unit (e.g., subframe). In addition, the “specifictime interval” may be expressed as time information (e.g., continuous ordiscontinuous time information configured in the form of a subframebitmap) indicating the time to start muting and the time after whichmuting ends based on a reference time clearly known to the TPs. Inaddition to the aforementioned subframe bitmap form, a time (e.g., aspecific subframe index) at which the “specific time interval” starts orthe number of cycles completed by the subframe bitmap before the“specific time interval” ends at a certain time (e.g., a specificsubframe index) may be explicitly indicated.

To express such “specific time interval”, a frame number (e.g., a systemframe number (SFN)) at which a CoMP operation (muting/non-muting, etc.)is applied (or started) may be used. For example, the CoMP operation maybe applied in a radio frame explicitly indicated by an SFN contained inXn-signaling. In this case, the frame number (e.g., SFN) may be definedbased on timing of a TP transmitting Xn-signaling. Alternatively, if theTP transmitting Xn-signaling is aware of information about timing of aTP receiving the Xn-signaling, the SFN value may be set to a value basedon timing of the TP receiving the Xn-signaling and transmitted.

In addition, the “specific band” may be set to a value expressed in apredetermined frequency unit (e.g., RB unit).

2-Way Xn-Signaling for Initiation of SSPM

Xn-signaling for SSPM may be defined as 2-way signaling implemented in amanner that TP1 makes a request to TP2 for performing muting (i.e.,resource coordination) and TP2 sends a response to TP1. In this case,the response message transmitted by TP2 may be delivered to TP1 andother TPs (e.g., TP3, TP4, . . . ) in a multicast/broadcast manner, ormay be individually delivered to TP 1 and other TPs by TP2 in a unicastmanner.

Herein, the information contained in the request message transmitted byTP1 may be a message requesting that TP2 perform muting for a “specificband” in a “specific time interval”.

For the “specific time interval” and “specific band”, the same featuresof 1-way Xn-signaling for SSPM described above may be applied.

In this example, a “specific condition” for transmission of the requestmessage from TP1 may be defined.

For example, TP1 may pre-provide configuration of a plurality of CSIprocesses for UEs associated therewith through RRC signaling (on theassumption that a delay greater than or equal to 100 ms may occur in RRCsignaling), and continuously receive feedback for the respective CSIprocesses. Then, if a difference between CQIs fed back for different CSIprocesses becomes greater than or equal to a predetermined referencevalue, TP1 may transmit the request message. The plurality of CSIprocesses may include CSI process 1 and CSI process 2. For example, CSIprocess 1 may be configured by a combination of NZP CSI-RS1 and CSI-IM1,which reflects a situation in which TP2 performs non-muting, and CSIprocess 2 may be configured by a combination of NZP CSI-RS1 and CSI-IM2,which reflects a situation in which TP2 performs muting. If thedifference between CQI1 fed back for CSI process 1 and CQI2 fed back forCSI process 2 is greater than or equal to a predetermined referencevalue, this may mean that the condition for transmission of the requestmessage is satisfied.

Such “specific condition” may also involve information about loadbetween TP1 and TP2. For example, the request may be allowed only if thevalue of the load situation of TP2 is well below a predeterminedreference value. Alternatively, if the value of the load situation ofTP2 is greater than the predetermined reference value, TP2 may rejectthe delivered request.

The “specific condition” may be defined such that priorities are presetbetween the TPs (e.g., TP1 may be preset as a master, and TP2 may bepreset as a slave), and thus when TP1 sends the request according to thepriorities, TP2 must conform to the request.

If TP1 is pre-provided with information pre-confirming that TP2 willaccept the request, through information such as the loading information,information about one or more CSI-RS configurations, information aboutone or more CSI-IM (or IMR) configurations, or DMRS configurationinformation, which is pre-exchanged through Xn-signaling, the SSPMoperation may be initiated simply by a muting request for SSPM which TP1sends to TP2 (namely, without a response from TP2).

If a specific condition for transmission of the request message isdefined as above, and the request message is transmitted from TP1 as thecondition is satisfied, TP2 receiving the request message may accept therequest. The case in which TP2 should obey the request of TP1 if aspecific condition is satisfied (or the case in which TP2 obeys therequest without sending a response message to TP1) may be calledconditional 1-way Xn-signaling.

Xn-Signaling During SSPM Operation

If SSPM is initiated through 1-way or 2-way Xn-signaling in a specificband in a specific time interval, SSPM may be defined as automaticallyending when the time interval ends. Alternatively, the time interval maybe extended through additional Xn-signaling (e.g., 1-way signaling or2-way signaling) before the time interval ends. The information aboutthe extended time interval may be updated with a new type of timeinformation, and the band information may be updated with a new type ofband information.

For example, CSI process 1 may be configured by a combination of NZPCSI-RS1 and CSI-IM1, which reflects a situation in which TP2 performsnon-muting, and CSI process 2 may be configured by a combination of NZPCSI-RS1 and CSI-IM2, which reflects a situation in which TP2 performsmuting. In this case, before SSPM is initiated, TP1 may transmit a PDSCHto the UE through scheduling based on a feedback report on CSI process 1from the UE (i.e., configuration of MCS1 based on CQI1). In the timeinterval in which SSPM is initiated, TP1 may transmit an SSPM-PDSCH tothe UE through scheduling based on a feedback report on CSI process 2from the UE (i.e., configuration of MCS2 (e.g., an MCS higher than MCS1)based on CQI2 in which muting of TP2 is reflected. In this way, the TPtransmitting a PDSCH to the UE receives both feedback reports on CSIprocess 1 and CSI process 2, but may apply PDSCH scheduling based on CSIfeedback information about a specific CSI process depending on whetheror not the time interval is an SSPM interval.

Xn-Signaling for Feedback for SSPM

Xn-signaling for feeding back usage information about how much of themuting band of neighboring TPs the TP transmitting the SSPM-PDSCH hasutilized to schedule a CoMP UE to transmit the SSPM-PDSCH may beadditionally defined in or after the SSPM time interval.

For example, usage feedback information indicating the portion (e.g.,percentage proportion) of resources which are used for scheduling for aUE (or CoMP UE) needing coordination between TSs participating in SSPMamong the resources indicated by the coordination (e.g., resourcesdefined by at least one of the frequency domain, time domain, powerdomain and space domain) may be exchanged between the TPs in the form ofXn-signaling. In addition, usage feedback information indicating theportion (e.g., percentage) of resources which are used for schedulingfor a UE (or non-CoMP UE) that does not need coordination between theTSs participating in SSPM among the resources indicated by thecoordination may be exchanged between the TPs in the form ofXn-signaling.

Xn-signaling may be defined such that the CoMP UE usage feedbackinformation and non-CoMP UE usage feedback information are transmittedtogether. The proportion of the resources used for a UE (i.e., CoMP UE)having the benefit may be indicated among the resources indicated by thecoordination between the TPs and the information may be used for thenext SSPM resource configuration only when the CoMP UE usage feedbackinformation and non-CoMP UE usage feedback information are providedtogether. Accordingly, by checking the usage information indicatingwhether time intervals and bands in which neighboring TPs perform mutingare actually used for scheduling a corresponding CoMP UE, excessiveconsumption of muting resources may be prevented, and the correspondingresources may be utilized in performing data transmission to other UEs.Thereby, overall network performance may be enhanced.

CoMP Network Architecture and Xn-Signaling for Resource Coordination

In various examples of the present invention, one of a plurality of TPsparticipating in the CoMP operation or a specifically defined centralcontrol node (CCN) may perform coordination decision and deliver acoordination result (or resource coordination result). A coordinationarchitecture having no CCN to control the TPs participating in the CoMPoperation may be called a distributed coordination architecture, and acoordination architecture having a CCN may be called a centralizedcoordination architecture. For clarity, Xn-signaling is simply describedas being performed between specific TPs in various examples of thepresent invention. The Xn-signaling may refer to Xn-signaling betweenTPs of the distributed coordination architecture or Xn-signaling betweena CCN and a TP of the centralized coordination architecture.

Regarding the proposed details described in the Xn-signaling for SSPM,Xn-signaling for indicating the resource coordination request orresource coordination result may be designed to indicate specificindexes on a specific frequency-time resource basis (e.g., PRB basisand/or subframe basis) among NW-CSI-IM indexes known to a sender TP (orsender eNB) as shown in Table 8 below.

TABLE 8 IE/Group Name Semantics description Indication of resource PerPRB (and/or per subframe index coordination (notice/result based on asubframe bitmap), or request) NW-CSI-IM index(es) are listed, meaningthe transmission assumptions (including transmitted power and/orprecoding information) on the REs corresponding to the listed NW-CSI-IMindexes can be assumed to be the same on the indicated PRB (and/orsubframe index).

As shown in Table 8, semantics of the NW-CSI-IM indexes indicatedthrough Xn-signaling may be interpreted as follows.

A sender eNB transmitting NW-CSI-IM indication information may informreceiver eNB(s) receiving the same that the NW-CSI-IM indicationinformation is about a resource coordination notice/result, or apredetermined selector bit for informing of a resource coordinationrequest may exist. For example, the NW-CSI-IM indication information maybe interpreted as indicating a resource coordination notice/result or aresource coordination request depending on the value of the selector bitcontained in the NW-CSI-IM indication information. Alternatively, theNW-CSI-IM indication information may be defined to be interpreted asinformation about a resource coordination notice/result if there is noseparate indication (namely, to be interpreted, by default, asinformation indicating a resource coordination notice/result). In thiscase, to indicate that the NW-CSI-IM indication information is about aresource coordination request, special indication information needs tobe included. (For example, the NW-CSI-IM indication information may beinterpreted as indicating a resource coordination request if a specificfield has a special value. Otherwise, the information may be interpretedas indicating a resource coordination notice/result). Alternatively,separate Xn-signaling formats may be designed for the resourcecoordination notice/result and the resource coordination request.

NW-CSI-IM Indication Information Indicating Resource CoordinationNotice/Result

The NW-CSI-IM indication information may be interpreted as indicatingthat it can be assumed that the property (e.g., transmit power and/orprecoding information) of a (interference) signal which a sender eNBtransmits at an RE location (time/frequency resource location) set onNW-CSI-IM index(es) listed in the NW-CSI-IM indication information isthe same as the property of a signal (e.g., PDSCH) that the sender eNBactually transmits on an indicated PRB and/or subframe index location.

This interpretation of the NW-CSI-IM indication information may bemainly applied to the distributed coordination architecture. Forexample, when the sender eNB transmits a signal in the form ofinformation of one or more CSI-IM (or IMR) configurations as shown inTable 6 or 7 on a specific NW-CSI-IM resource through “non-muting”, thesender eNB may notify the receiver eNB(s) that a signal property appliedto the NW-CSI-IM resource is the same as the signal property applied toa specific frequency/time resource (or another frequency/time resourcemap). When other eNBs having received this notice information perform UEscheduling on a specific frequency/time resource indicated by thereceived information, they may determine or select a precoder, MCS andthe like to be applied to DL transmission, based on the CSI feedbackinformation provided by the UE for an NW-CSI-IM index that the sendereNB has signaled as information associated with the specificfrequency/time resource.

In addition, if a receiver eNB receives NW-CSI-IM indication informationfrom multiple sender eNBs through Xn-signaling with respect to aspecific frequency/time resource map, the receiver eNB may determinespecific NW-CSI-IM index(es) indicated in common as an intersection ofNW-CSI-IM indexes indicated by the information provided by the sendereNBs. Thereby, CSI process indexes including the specific NW-CSI-IMindexes indicated in common may be determined, and the receiver eNB mayreceive a configuration of the CSI process indexes and consider the UEperforming CSI feedback as a scheduling target. That is, given multipleeNBs set to “non-muting” for specific NW-CSI-IM indexes (e.g., NW-CSI-IMindexes 4, 6 and 7 in Table 6 or 7) to apply a specific signal on thecorresponding resource, channel information recognized from a CSIfeedback report which is based on the property of interference measuredby the UE on the indicated NW-CSI-IM index(s) may become as similar tothe channel state on a specific time/frequency resource used for UEscheduling as possible only when UE scheduling is performed for aspecific time/frequency resource map on which NW-CSI-IM indicationinformation has been received from as many eNBs as possible.

The NW-CSI-IM indication information may also be defined or configuredto be transmitted to eNBs belonging to a specific eNB set (e.g., a CoMPcluster) in a multicast/broadcast manner. Herein, the specific eNB setmay be predefined, or may be determined or configured throughpre-negotiation between specific eNBs (or eNB sets) through separateXn-signaling. That is, the NW-CSI-IM indication information may deliverIEs as shown in Table 8 through multicast/broadcast signaling directedto multiple eNBs belonging to a CoMP cluster rather than through unicastsignaling sent to one receiver eNB. Thereby, the multiple eNBs receivingthis information may indicate NW-CSI-IM indexes associated with eachother to a frequency/time resource map as similar to the frequency/timeresource map indicated by the sender eNB as possible in the best effortform and exchange the same sequentially (or in series) throughXn-signaling. Preferably, for example, for PRBs showing no noticeabledifference in frequency selectivity, the receiver eNB having receivedthe NW-CSI-IM indication information selects the same NW-CSI-IM indexes,if possible, with reference to the frequency/time resource map of thesender eNB that has provided the Xn-signaling first, and transmitsXn-signaling directed to other eNBs. For example, in Table 6 or 7, ifeNB2 indicates “NW-CSI-IM indexes 3, 4 and 7” for a specificfrequency/time resource map, eNB3 receiving the indexes conforms to aform as similar to the frequency/time resource map as possible (by, forexample, configuring a frequency/time resource map such that as manyfrequency/time resources as possible overlap each other although somefrequency/time resources may be the same or different), and indicate“NW-CSI-IM indexes 2, 4 and 6” to eNB1 through Xn-signaling. When eNB1receives NW-CSI-IM indication information from eNB2 and eNB3, eNB1 mayselect NW-CSI-IM index 4 as an intersection between the information, andconsider a UE for which a specific CSI process including the selectedindex is configured as a scheduling target first.

In addition, regarding the frequency/time resource map, it may beeffective to pre-divide a CoMP-allowed region and a CoMP-disallowedregion through separate Xn-signaling and align CoMP-allowed regions ofthe eNBs as much as possible through negotiation between the eNBs. Thatis, the eNBs may predetermine a specific frequency/time resource towhich CoMP is not applied, in consideration of a guaranteed bit rate(GBR) bearer, and pre-exchange this information to utilize theinformation in pre-negotiating the CoMP-allowed regions. Morespecifically, a subset of eNBs greatly affecting a CSI-IM resource foreach NW-CSI-IM index may be pre-constructed/pre-configured for eachNW-CSI-IM index (for example, a subset may bepre-constructed/pre-configured with eNBs that geographically neighboreach other), and negotiation for alignment of the frequency/timeresource map may be mainly performed between eNBs. For example, even ifXn-signaling for the negotiation for the frequency/time resource map ismulticast/broadcast to a specific eNB set such as the CoMP cluster, eNBshaving higher priorities as negotiation targets may be separatelydesignated.

To allow the operations above to be smoothly performed, Xn-signalingsshould avoid overlapping each other within a specific eNB set such asthe CoMP cluster as described above. To this end, the eNBs in thespecific eNB may take turns sequentially (serially) to transmitXn-signaling according to a pre-defined or pre-configured period and/oroffset.

NW-CSI-IM Indication Information Indicating Resource CoordinationRequest

The NW-CSI-IM indication information may be interpreted as requestingthat the property (e.g., transmit power and/or precoding information) ofa (interference) signal which a receiver eNB transmits at an RE location(time/frequency resource location) set on NW-CSI-IM index(es) listed inthe NW-CSI-IM indication information should be the same as the propertyof a signal (e.g., PDSCH) that the receiver eNB actually transmits on anindicated PRB and/or subframe index location.

In the case where the NW-CSI-IM indication information indicates aresource coordination request, the sender eNB used in the case where theNW-CSI-IM indication information indicates a resource coordinationnotice/result is switched to the receiver eNB. In addition, the proposedexamples of the case of the NW-CSI-IM indication information indicatinga resource coordination notice/result may be applied as examples of thecase of the NW-CSI-IM indication information indicating a resourcecoordination request by switching the sender eNB to the receiver eNB andvice versa.

Additionally, once the receiver eNB receives the NW-CSI-IM indicationinformation indicating a resource coordination request, the receiver eNBmay send a response message through signaling indicating acceptance orrejection of the request.

The response message may simply indicate acceptance or rejection, butthe intention of acceptance or rejection may be delivered using anothermethod.

For example, Xn-signaling for “Rejected” may be replaced by theNW-CSI-IM indication information indicating the resource coordinationnotice/result. In this case, the receiver eNB having received theresource coordination request may be understood as delivering, to thesender eNB having transmitted the resource coordination request, aresource coordination notice/result indicating “Rejected” for therequest and reconfigured in a different form by the receiver eNB throughXn-signaling.

Xn-signaling for “Accepted” may be configured to include a case wherethe receiver eNB does not transmit response signaling to the sender eNB(namely, a response is omitted). That is, if the sender eNB sendsNW-CSI-IM indication information indicating a resource coordinationrequest to the receiver eNB through Xn-signaling, the request may bedefined or configured to be accepted by default as long as there is noseparate response from the receiver eNB. This operation may beeffectively utilized in the centralized coordination architecture. Forexample, when a CCN (or a specific eNB (e.g., Macro-eNB) serving as aCCN; hereinafter, referred simply to as CCN) delivers NW-CSI-IMindication information indicating a resource coordination request toother eNBs through Xn-signaling, a receiver eNB receiving theinformation may be configured not to signal a response message orconfigured to signal a response message indicating “accepted” dependingon the type of the sender eNB (e.g., only if the sender eNB is a CCN ormacro-eNB). In this case, the Xn-signaling transmitted from the sendereNB takes the form of a resource coordination request, but substantiallyfunctions as a command for resource coordination. Thereby, a centralizedcoordination architecture including a sender eNB (e.g., a CCN) and otherreceiver eNBs (e.g., non-CCNs) may be configured.

In a distributed coordination architecture, on the other hand, if areceiver eNB having received NW-CSI-IM indication information indicatinga resource coordination request sends a response message indicatingacceptance of the request, the sender eNB having transmitted theNW-CSI-IM indication information indicating the resource coordinationrequest may determine or select a precoder, MCS and the like to beapplied to DL transmission, based on the CSI feedback information abouta specific NW-CSI-IM index associated with a specific frequency/timeresource provided by a corresponding UE when the sender eNB schedulingthe UE on the specific frequency/time resource indicated by theNW-CSI-IM indication information.

Centralized Coordination Architecture Xn-Signaling

Hereinafter, a benefit metric will be described as additionalXn-signaling which can be advantageously used in various examplesproposed in the present invention, in particular, a centralizedcoordination architecture. The benefit metric may be a UE schedulingmetric or utility metric of a specific frequency/time resource map sentfrom each eNB to the CCN. In the description below, the term utilitymetric will be mainly used, but this term should be understood as a termrepresenting UE scheduling metric or benefit metric.

A utility metric may be defined as a value for the data rate orthroughput that may be expected when a specific UE is scheduled on aspecific frequency/time resource (e.g., a resource defined on the PRBand/or subframe index basis). For example, the utility metric may bedefined as a value obtained by dividing a data rate (or throughput)expectable for a specific UE by the average data rate (or averagethroughput) of the UE. In addition or alternatively, the utility metricmay be defined as a value for a data rate (or throughput) expectable fora specific UE that is derived in consideration of QoS of the UE (e.g., avalue calculated according to a specific function predefined orpre-configured according to QoS of the UE).

For example, if the utility metric value increases, this may mean thatperforming UE scheduling on the corresponding frequency/time resource isadvantageous to the eNB. Accordingly, if a sender eNB sends such utilitymetric to a CCN through Xn-signaling, this may be interpreted as meaningthat the sender eNB provides the CCN with information indicating thatthe sender eNB prefers performing data (e.g., PDSCH) transmission toperforming muting on a frequency/time resource having a high utilitymetric value.

A plurality of utility metrics may be sent for a specific frequency/timeresource through Xn-signaling. In this case, each utility metric mayhave a value calculated on the assumption of different CoMP hypothesis.Herein, the different CoMP hypothesis may mean a different interferenceenvironment, may be defined as a pattern indicating whether or notmuting is performed by each eNB, or may mean a different CSI processunit.

As a method to express different CoMP hypotheses that the sender eNBassumes through Xn-signaling, the format of one or more CSI-IM (or IMR)configurations information as shown in Table 6 or 7 may be employed. Forexample, a utility metric value may be calculated for each“NW-CSI-process index” and sent through Xn-signaling, or may calculatedfor each “NW-NZP-CSI-RS index and/or NW-CSI-IM index” and sent throughXn-signaling.

For example, a utility metric value may be calculated and sent throughXn-signaling on the assumption of data (e.g., PDSCH) transmission basedon CSI feedback of a corresponding UE per specific frequency/timeresource (e.g., PRB and/or subframe index) according to specificNW-CSI-process index(es), as shown in Table 9 below.

TABLE 9 IE/Group Name Semantics description Utility metric (or UE PerPRB (and/or per subframe index based scheduling metric, or on a subframebitmap), benefit metric) pair(s) of {utility metric(U bits),NW-CSI-process index(es)} are listed, meaning the utility metric valueis calculated assuming the (PDSCH) transmission based on on the CSIfeedback according to the indicated NW-CSI-process index).

As shown in Table 9, a utility metric may have the size of U bits, and apair of a utility metric and NW-CSI-process index(es) may beXn-signaled.

Another utility metric calculated on the assumption of differentNW-CSI-processes may also be Xn-signaled. That is, as shown in Table 9,one pair or a plurality of pairs of {utility metric, NW-CSI-processindex(es)} may be Xn-signaled.

As one NW-CSI-process index is configured by a combination of oneNW-NZP-CSI-RS index and one NW-CSI-IM index, calculating a utilitymetric for each NW-CSI-process index may mean that a channel (or desiredsignal) is measured based on the NW-NZP-CSI-RS indicated by aNW-CSI-process index, interference is measured based on the NW-CSI-IMindicated by the NW-CSI-process index, and a utility metric iscalculated assuming that a PDSCH is transmitted based on CSI feedbackinformation (e.g., RI, PMI, and CQI) calculated/generated based on theresults of the measurements.

A CCN may receive Xn-signaling containing such utility metric frommultiple eNBs, and perform global optimization within a specific eNB set(e.g., CoMP cluster) including the eNBs, based on all the receivedinformation. Thereby, NIB CoMP operation may be efficiently performed bytransmitting the eNBs Xn-signaling containing information indicating aresource coordination request from each eNB (e.g., Xn-signalingcontaining NW-CSI-IM indication information indicating a resourcecoordination request (which is substantially a resource coordinationcommand)).

For example, if the CCN selects the highest utility metric value for aspecific frequency/time resource as a resource coordination result, theCCN may recognize specific NW-CSI-IM index(es) associated withcorresponding NW-CSI-process index(es) because the CCN is already awareof the NW-CSI-process index(es) forming the basis of calculation of theselected utility metric (i.e., a pair of {utility metric, NW-CSI-processindex(es)} shown in Table 9). Thereby, the CCN may configureXn-signaling in the form of NW-CSI-IM indication information indicatinga resource coordination request (or resource coordination command) andtransmit the same to the eNBs.

As described above, in the Table 9, the “NW-CSI-process index(es)” maybe replaced by “NW-NZP-CSI-RS index(es) and/or NW-CSI-IM index(es)”. Inthis case, a utility metric IE may be defined as shown in Table 10below.

TABLE 10 IE/Group Name Semantics description Utility metric (or UE PerPRB (and/or per subframe index scheduling metric, or based on a subframebitmap), benefit metric) pair(s) of {utility metric(U bits),NW-NZP-CSI-RS index(es) and/or NW-CSI-IM index(es)} are listed, meaningthat the utility metric value is calculated assuming the (PDSCH)transmission based on the CSI feedback according to the indicatedNW-NZP-CSI-RS index(es) and/or NW-CSI-IM index(es).

The embodiment employing Xn-signaling for a utility metric IE defined inTable 9 may be applied as an embodiment employing “NW-NZP-CSI-RSindex(es) and/or NW-CSI-IM index(es)” in place of “NW-CSI-processindex(es)” in Table 8.

Specifically, this may mean that each eNB measures a channel (or desiredsignal) based on the indicated NW-NZP-CSI-RS, measures interferencebased on the indicated NW-CSI-IM, and calculate a utility metricassuming that a PDSCH is transmitted based on CSI feedback information(e.g., RI, PMI, and CQI) calculated/generated based on the results ofthe measurements.

Alternatively, in the example of Table 9, Xn-signaling may be configuredin the form of one or more pairs of {utility metric (U bits), NW-CSI-IMindex(es)}, omitting the information indicating the NZP-CSI-RSindex(es). In this case, the NW-NZP-CSI-RS index(es) forming the basisof calculation of the utility metric may be interpreted as beingseparately signaled by the sender eNB transmitting the utility metric,and the specific NW-NZP-CSI-RS index(es) being configured/transmitted bythe sender eNB may be interpreted as being implicitly indicated.

Xn-Signaling of Information Similar to Utility Metric

In place of the Xn-signaling operation for a utility metric (or UEscheduling metric, or benefit metric) described in the examples above,Xn-signaling of other similar information (e.g., preference rating orpriority map) may be applied. Hereinafter, a detailed description willbe given of the utility metric, preference rating and priority map.

As described above, the utility metric is defined as a value indicatinga data rate (or throughput) that is expectable when a specific UE isscheduled on a specific frequency/time resource (e.g., PRB unit and/orsubframe index unit). Further, a calculated value of the utility metricmay be expressed as a value mapped to the calculated value according toa predefined quantization reference. However, the eNB may be differentlyimplemented among network venders, and thus it is very likely that thecalculation methods for the utility metric for the eNBs are notidentical to each other. If a network operator configures a CoMP clusterincluding eNBs implemented by different network vendors, utility metricvalues calculated and Xn-signaled by the respective eNBs may be valuesexpressed by different references, and it may be impossible to comparethe values. Accordingly, a comparison reference similar to but simplerthan the utility metric may be used.

The preference rating or priority map may be configured as a simplifiedlevel (e.g., defined as indicating one of four levels) in contrast withthe utility metric. Similar to the utility metric described in Table 9or 10, the preference rating or priority map may be paired with an NWCSI index. Specifically, one or more pairs of {preference rating (orpriority map), NW-CSI-process index(es)}, one or more pairs of{preference rating (or priority map), NW-CSI-IM index(es)}, or one ormore pairs of {preference rating (or priority map), NW-NZP-CSI-RSindex(es) and/or NW-CSI-IM index(es)} may be listed in Xn-signaling.

The preference rating (or priority map) does not need a metric whichdepends on a scheduler algorithm which may change according to animplemented eNB, and may be utilized to express a simplified preferenceor priority. In expressing the preference or priority, the preference orpriority may be utilized in a CoMP cluster as a value comparable betweeneNBs implemented by different network vendors by allowing the networkoperator rather than the value network vendor to insert the same in asoftware-based algorithm.

The sender eNB sends signaling such as the utility metric, UE schedulingmetric, benefit metric, preference rating, and priority map to informother eNBs of utility/benefit/preference of the sender eNB assuming aspecific CoMP hypothesis (i.e., operation of each eNB (e.g., muting,transmission assumptions, etc.) in a CoMP cluster) indicated by anNW-CSI-process index (or NW-CSI-IM index). This operation may beinterpreted as informing other eNBs of an operation that is preferablein view of the sender eNB when the specific CoMP hypothesis is applied.

The proposed signaling such as the utility metric, UE scheduling metric,benefit metric, preference rating, and priority map is clearly differentfrom the conventional inter-eNB signaling in that the sender eNB informsof not only the operation thereof but also operations of other eNBs inthe CoMP cluster (i.e., operations of other eNBs which the sender eNBdetermines to be preferable in terms of optimization of networkperformance and/or operations of other eNBs which the sender eNBdesires), rather than conforming to a basic principle of signalingbetween eNBs in the conventional art (i.e., the principle stating thatthe sender eNB informs other eNBs of only the operation thereof and isnot involved in operations of the other eNBs).

Xn-Signaling of Utility Metric Information

In addition to or in place of Xn-signaling the utility metric as shownin Table 9 or 10, element information for calculating the utility metricmay be exchanged between eNBs through Xn-signaling on the frequency/timeresource basis. In the centralized coordination architecture, elementinformation for calculating the utility metric may be designed to betransmitted from eNBs to the CCN.

The element information may include at least one of the followingexamples:

-   -   One or more sets of CSI reports (e.g., RI, PMI, CQI) of UEs to        be scheduled    -   One or more sets of measurement reports (e.g., RSRP) of UEs to        be scheduled    -   Sounding reference signal (SRS) reception power of UEs to be        scheduled    -   User perceived throughput; UPT) of UEs to be scheduled    -   Proportional fair (PF) metric of UEs to be scheduled    -   QoS class identifier (QCI) of UEs to be scheduled.

In the examples above, the “UEs to be scheduled” may be defined orconfigured to be interpreted as meaning that information about specificUEs, which the eNB desires to schedule on a corresponding frequency/timeresource, is included in the element information. That is, thisoperation may be understood as delivering the element information aboutthe best UE or representative UE to the receiver eNB rather thandelivering the element information about all individual UEs served bythe sender eNB. Thereby, Xn-signaling overhead may be significantlyreduced. In addition, overall optimization may be readily performed inthe CoMP cluster even if element information about only some UEs iscollected by the CCN.

More specifically, in the examples above, the “UEs to be scheduled” maybe interpreted as “a set of (active) UEs”. This may be interpreted asmeaning that element information about all active UEs is signaled orthat element information about some of active UEs (which may be selectedby the sender eNB) is signaled.

Even if element information about some UEs is signaled, the minimumnumber of UEs in the “set of UEs” may be set to 1. That is, the sendereNB may be defined to signal element information about at least one UE.For example, when it is requested or indicated according to theXn-signaling protocol (by, for example, a predetermined invoke message)that the element information as above should be transmitted, or when thesender eNB attempts to transmit the element information throughinter-eNB Xn-signaling for the first time, the minimum number of UEs inthe “set of UEs” may be set to 1.

Alternatively, the minimum number of UEs in the “set of UEs” may beallowed, on the Xn-signaling protocol, to be set to 0 according to thetype of the element information. For example, the minimum number of UEsbelonging to UEs (i.e., “a set of UEs”) to be scheduled in “one or moresets of CSI reports (e.g., RI, PMI, CQI) of UEs to be scheduled” may bedefined to be 1, and the minimum number of UEs belonging to UEs (i.e.,“a set of UEs”) to be scheduled in “one or more sets of measurementreports (e.g., RSRP)” may be defined to be 0. This may be interpreted asmeaning that CSI information about at least one UE needs to be providedto another eNB, but RSRP information may be optionally provided inperforming Xn-signaling for element information. Alternatively, if RSRPinformation is not provided, (i.e., RSRP information about zero UE isprovided), this may mean that the previously provided RSRP informationabout specific UEs does not change, and thus the corresponding value isnot updated.

In addition, the UEs belonging to the “UEs to be scheduled” or “set ofUEs” may be selected from among UEs satisfying minimum requirements. Forexample, CoMP configurable UEs (e.g., UEs set to transmission mode 10 ora higher mode), UEs for which two or more CSI processes are configured,or UEs for which the maximum number of CSI processes which aresupportable according to UE capability information is greater than orequal to 2 may be defined to be included in the “set of UEs”.

In addition to the examples of element information related to theutility metric, transmission buffer information (e.g., “Status oftransmission queues”) may be Xn-signaled.

The status of transmission queues information may be used to minimizedelay in packet delivery. For example, as the length of a queueincreases, the utility metric value may increase. For example, byXn-signaling the length information about a transmission queue of aneNB, a CCN may assign a high utility metric value if the CCN determinesthat the queue is long (this may mean that a maximum delay schedulingalgorithm is applied).

The sender eNB may transmit the status of transmission queuesinformation through Xn-signaling at intervals of T ms. In this case, thestatus of transmission queues may include one of the following pieces ofinformation at a specific time:

-   -   Information indicating a current transmit buffer status for each        specific UE;    -   Information indicating the amount of data (number of packets)        that has been scheduled since the previous Xn-signaling time        (e.g., the time before T ms);    -   Information indicating the amount of new data (number of        packets) that has been additionally stacked in the buffer since        the previous Xn-signaling time (e.g., the time before T ms);    -   Information indicating queue status accumulated in the        transmission queue up to the current time.

Using one or more of the information, a network node (e.g., CCN)receiving Xn-signaling of the information may recognize the amount ofdata stacked in the sender eNB transmitting the information, and assigna higher weight to an eNB in which a larger amount of data is stacked atthe time of resource coordination/assignment.

Meanwhile, in the “integrated Xn-signaling” described below,Xn-signaling information referred to as “benefit metric” or “preferencerating value” may include “transmit buffer and queue statusinformation”. The examples included in the “status of transmissionqueues” information described above may be defined or configured to betransmitted in the form of “transmit buffer and queue statusinformation”. For example, in the “transmit buffer and queue statusinformation”, the “transmit buffer status” information may mean“information indicating current transmit buffer status for each specificUE”, and the “queue status” information may mean “information indicatingthe queue status accumulated in the transmission queue up to the currenttime”. As such, some or a combination of a plurality of specificexamples of the “status of transmission queues” may be transmittedthrough Xn-signaling as content of a message for delivering variouskinds of buffer status-related information.

Additional Example 1 of Inter-NIB CoMP eNB Signaling

The following information may signaled on an Xn interface (e.g., X2interface) between eNBs for NIB CoMP:

-   -   CoMP hypothesis. The CoMP hypothesis may include hypothetical        resource allocation for at least a receiver node in the        time/frequency;    -   One or more sets of CSI information (RI, PMI, CQI) about a set        of UEs;    -   One or more measurement reports (RSRP) on a set of UEs;    -   Improved RNTP (Enhanced Relative Narrowband Tx Power). The        information configuration granularity of the improved RNTP may        be extended in the frequency/time domain. In addition,        information in the improved RNTP may include a transmit power        threshold only for a sender eNB, and be configured in multiple        levels. To exchange the utility status of an indicated        frequency/time resource, the conventionally defined status        report may be signaled between eNBs;    -   Benefit metric.

Hereinafter, details that need to be specifically defined in theXn-signaling information will be described.

CoMP Hypothesis

The CoMP hypothesis includes hypothetical resource allocation for atleast a receiver node in the time/frequency domain, which is intended tosupport centralized coordination. Signaling of such CoMP hypothesis maybe used to indicate the result of resource coordination determined by aCCN, or may be used as a hypothetical condition assumed for benefitmetric signaling (without a time/frequency configuration granularity).

How to respond to the received CoMP hypothesis signaling depends onimplementation of the receiver eNB, or the receiver eNB may send thetransmitter node feedback (e.g., YES/NO) indicating acceptance/rejectionof the hypothesis.

The configuration granularity and signaling period of a time/frequencydomain necessary for the CoMP hypothesis may be set on the PRB andsubframe basis and be indicated by an L-bit subframe. In considerationof different NIB delay and signaling periods, it is proposed that themaximum value of L be 10. A proper signaling period L for the CoMPhypothesis may differ between sender nodes, and accordingly the value ofL may be included in the CoMP hypothesis signaling information, or thereceiver node may request the period value (i.e., the L value). The CoMPhypothesis information may include cell-specific power assignmentinformation (information indicating whether or not muting is performed,information indicating a power level, or the like) and be identified bya cell ID.

Benefit Metric Associated with CoMP Hypothesis

The benefit metric may be defined as follows.

The benefit metric, which is associated with the CoMP hypothesis, isinformation quantifying the benefit that a cell of the sender nodeexpects in performing scheduling on the assumption of the associatedCoMP hypothesis.

The cell-specific benefit metric is calculated as the maximum value inthe result of a function that the operation defines from elementinformation given for each of active UEs in the corresponding cell. Theelement information may be a CSI report (RI, PMI, CQI) set, one or moremeasurement reports (RSRP), average user throughput, transmit buffer andqueue status information, and QCI that correspond to the associated CoMPhypothesis.

FIG. 13 illustrates a benefit metric signaled together with a CoMPhypothesis for a frequency/time resource map.

In FIG. 13, the CoMP hypothesis may be indicated by a power assignmentlist for individual eNBs. The power assignment list may be configured toexplicitly indicate the power assignment value for eNB1, the powerassignment value for eNB2, . . . , and the power assignment value foreNB N. Alternatively, the CoMP hypothesis may be indicated in a simplerform such as an NW CSI-IM index. That is, one index value may indicateoperation of individual eNBs.

The benefit metric may be signaled together with the associated CoMPhypothesis without a time/frequency configuration granularity.Specifically, the signaled benefit metric means a quantized benefitvalue which the cell of the sender node expects in performing schedulingon the assumption of the associated CoMP hypothesis (e.g., amuting/non-muting pattern of a neighboring cell).

The sender node may signal a plurality of benefit metrics, and each ofthe benefit metrics is associated with a different CoMP hypothesis.Thereby, each benefit metric may represent preference rating of acorresponding CoMP hypothesis (information indicating not only operationof the sender eNB but also operations of the other eNBs) in view of thesender eNB.

As the benefit metrics are signaled together with CoMP hypotheses, thetransmission period of the benefit metrics may be configured to be equalto the transmission period (e.g., period value L) of the CoMPhypotheses.

The information of a benefit metric may be defined as an integer valuebetween 0 and B (B>0). As the benefit metric is defined as a quantizedvalue considering all active UEs in a cell, B may be set to 100, forexample. As a simple example, a PF metric derived from at least one CSIreport set and average user throughput corresponding to an associatedCoMP hypothesis may be used to calculate the benefit metric. Herein, oneor more measurement reports (RSRP) may also be used to calculate CQI.Since the CQI is calculated not by a CCN but by a sender eNB, QCI oradditional information such as transmit buffer and queue statusinformation may be used. When benefit metrics associated with differentCoMP hypotheses reach the CNN from a plurality of sender nodes, the CCNmay use all the information provided from member eNBs to determineresource coordination. If determination of resource coordination isprovided from the CCN to the member eNBs, the benefit metrics may notneed to be signaled. That is, since the CCN functions to determineresource coordination in consideration of benefit metrics expected bythe member eNBs, benefit metrics expected by the CCN do not need to beprovided to the member eNBs. If signaling transmitted from a member eNBto the CCN and signaling transmitted from the CCN to the member eNB aredefined in an “integrated signaling format,” which will be describedlater, the benefit metric information may be set to a special valueindicating that the signaling is a notice/command type of resourcecoordination decision which the CCN transmits to the member eNB, may beomitted, or may be reserved.

Signaling of CoMP hypotheses and benefit metrics as above may be appliednot only to the centralized coordination architecture but also to thedistributed coordination architecture. For example, in the distributedcoordination architecture, when eNB1 is a sender and eNB2 is a receiver,the benefit metric signaling may be understood as resource coordinationrequest (or resource coordination recommendation) signaling givenconsidering the indicated CoMP hypothesis in view of eNB1. In this case,eNB2 may consider information received from eNB1 in determiningscheduling thereof. Specifically, eNB2 may consider that the informationabout operation of the sender eNB1 is guaranteed to be applied to eNB1later. Thereby, the receiver eNB2 may utilize a CSI feedback report of arelevant UE. The information about the operation of the receiver eNB2may be considered when eNB2 operates in a best effort manner. In thedistributed coordination architecture, lots of such signaling may beexchanged, and thus the receiver eNB2 may also consider informationabout operation of other eNBs in performing scheduling thereof. Forexample, the most commonly preferred CoMP hypothesis (i.e., a CoMPhypothesis to which a large number of eNBs has assigned a higher benefitmetric value than to the other CoMP hypotheses) may be used as anassumption on final scheduling decision of the receiver eNB2.

CSI and RSRP Information

One or more sets of CSI information and/or RSRP information about a setof UEs may be Xn-signaled for CoMP operation in both the centralizedcoordination architecture and the distributed coordination architecture.The aforementioned cell-specific benefit metric does not includeexplicit UE-specific information such as CSI reported together with UEidentification information (ID) and NW-CSI-process identificationinformation (ID) assumed for the CSI, and therefore this type ofinformation may be used for CoMP as additional information based onsignaling of the benefit metric information. For example, if CSIinformation including PMI of UEs to be scheduled by the sender eNB isprovided to other eNBs, the receiver eNB may consider CoMP operationincluding coordinated beamforming (CB) based on the CSI information.

Since signaling of UE-specific information as above causes largeoverload for Xn-signaling between eNBs, element information such as QCI,buffer status and average user throughput may not be simultaneouslyXn-signaled. Accordingly, the UE-specific signaling may be treated assupplementary or optional information.

Improved RNTP

Signaling of an improved RNTP is recognized as a notice of operation ofthe sender eNB related to power level and/or beamforming information ofthe sender eNB on an indicated frequency/time resource map, and thus thedistributed coordination architecture may be supported by NIB CoMP. Incontrast with existing RNTP/ABS (almost blank subframe) signaling, theresource configuration granularity is extended to the two-dimensionaldomain of a frequency-time resource map, multi-level power assignmentinformation is indicated, and indication information (e.g., precodinginformation) in the space domain is included in signaling.

The improved RNTP may include a transmit power threshold and afrequency/time domain 2-dimensional bitmap. Each bit of the2-dimensional bitmap may indicate that a power level below the thresholdis or is not guaranteed. The resource configuration granularity may bedefined as an RB unit in the frequency domain and as a subframe unit inthe time domain. For a 2-dimensional resource map, bitmaps for K RBs andL subframes may be designed as a K-bit bitmap and an L-bit bitmap. Inthis case, the K-bit bitmap may be valid only in subframes indicated inthe L-bit bitmap (e.g., subframes corresponding to bits set to 1). Usingonly one power threshold, rather than using multi-level powerthresholds, may be sufficient.

Integrated Xn-Signaling

Signaling indicating a result/notice/request/recommendation/command forinterference coordination mentioned in the description of “NW-CSI-IMIndication Information Indicating Resource Coordination Notice/Result”and “NW-CSI-IM Indication Information Indicating Resource CoordinationRequest” may be designed in one integrated Xn-signaling format.Hereinafter, the integrated signaling format will be referred to as aCoMP coordination CSI-IM map, namely CCC map. Table 11 shows an exampleof the CCC map.

TABLE 11 IE/Group Name Semantics description CoMP Per PRB (and/or persubframe index based Coordination on a subframe bitmap), CSI-IM map;NW-CSI-IM index(es) are listed, meaning CCC map the transmissionassumption for the sender eNB (including transmitted power and/orprecoding information) on the REs corresponding to the listed NW-CSI-IMindexes can be assumed tobe the same on the indicated PRB (and/orsubframe index), and the transmission assumptions for other eNBs withinthe CoMP cluster (including transmitted power and/or precodinginformation) on the REs corresponding to the listed NW-CSI-IM indexesare (highly) recommended to be assumed to be the same on the indicatedPRB (and/or subframe index).

The integrated CCC map as shown in Table 11 indicates operations of asender eNB, a receiver eNB and other eNBs in a CoMP cluster alltogether. That is, in the CCC map, transmission assumption of each eNB(transmit power (including execution of muting) and/or precodinginformation) may be known from NW-CSI-IM index(es) information listedaccording to respective specific frequency/time resources. Thetransmission assumption on the sender eNB may be interpreted as meaningthat the sender eNB will constantly maintain the transmission assumptionthereof on the indicated frequency/time resource. Additionally oralternatively, the transmission assumption for the receiver eNB may beinterpreted as meaning that the sender eNB (highly) recommends that thereceiver eNB should constantly maintain the transmission assumption onthe indicated frequency/time resource. Additionally or alternatively,the transmission assumption for other eNBs (i.e., the other eNBs in theCoMP cluster) may be interpreted as meaning that the sender eNB (highly)recommends that the corresponding eNBs should constantly maintain thetransmission assumption on the indicated frequency/time resource.

Accordingly, the receiver eNB may assume that operations of other eNBsare very likely to be performed according to the CCC map, and performfinal scheduling decision considering the corresponding CSI feedbackinformation in scheduling a UE having performed CSI feedback reportingon the corresponding NW-CSI-IM index(es).

In the centralized coordination architecture, CCC map signaling as shownin the Table 11 may be defined or configured to be transmitted by only aspecific eNB (e.g., the CCN or Marco-eNB). In this case, the receivereNB may assume that operations of other eNBs will be performed accordingto the CCC map, and perform final scheduling decision considering thecorresponding CSI feedback information in scheduling a UE havingperformed CSI feedback reporting on the corresponding NW-CSI-IMindex(es).

If a plurality of NW-CSI-IM indexes associated with a specificfrequency/time resource is indicated and the transmission assumption forthe receiver eNB (or other eNBs) differs between the indicated NW-CSI-IMindexes, operation of the receiver eNB (or other eNB) may be defined orconfigured to be interpreted as “don't care”. Alternatively, if three ormore NW-CSI-IM indexes are indicated, operation of the receiver eNB (orother eNBs) may be defined or configured based on a larger number ofindicated NW-CSI-IM indexes to which the same transmission assumption isindicated.

An integrated Xn-signaling format may be configured by including theutility metric (or preference rating, priority map, or benefit metric)information shown in Table 9 or 10 in the exemplary CCC map shown in theTable 11. An example of this configuration is shown in Table 12. Theterms utility metric, preference rating, and priority map mentionedabove will be collectively referred to as “benefit metric” in theexamples described below.

TABLE 12 IE/Group Name Semantics description CoMP Per PRB (and/or persubframe index based Coordination on a subframe bitmap), CSI-IM pair(s)of {NW-CSI-IM index(es), benefit metric} map; CCC map are listed,meaning the transmission assumption for the sender eNB (includingtransmitted power and/or precoding information) on the REs correspondingto the listed NW-CSI-IM indexes can be assumed to be the same on theindicated PRB (and/or subframe index), and the transmission assumptionsfor other eNBs within the CoMP cluster (including transmitted powerand/or precoding information) on the REs corresponding to the listedNW-CSI-IM indexes are (highly) recommended to be assumed to be the sameon the indicated PRB (and/or subframe index).

Description of Table 11 may be applied to Table 12. Additionally,“benefit metric” information may be provided according to indicatedNW-CSI-IM index(es) as well.

In the distributed coordination architecture, the integrated signalingof Table 12 may be interpreted as informing of operations (i.e., a CoMPhypothesis) of the respective eNBs in a CoMP cluster which arerecommended/desired by the sender eNB and additionally informing of howbeneficial the CoMP hypothesis is to the sender eNB.

In the centralized coordination architecture, if the sender eNB is a CCNor macro-eNB, the integrated signaling of Table 12 may be interpreted assending a command/notice of an operation (i.e., a CoMP hypothesis) thatthe respective eNBs in the CoMP cluster need to maintain. Each of theeNBs receiving the signaling may apply the transmission assumptionapplied on NW-CSI-IM index(es) to the indicated frequency/time resourcein the same manner. In this case, the “benefit metric” information ofthe integrated signaling format transmitted by the CCN does not maintainthe original semantics, but may be utilized as a selector bit reserved(or not included) in the integrated signaling format or proposed in thepresent invention (e.g., if the benefit metric information has apredetermined special value, the integrated signaling may function as aresource coordination command/notice. Otherwise, the benefit metricinformation may be used to identify signaling transmitted from membernetwork nodes to the CCN). However, the scope of the present inventionis not limited thereto. Information different from the benefit metricinformation may function as the selector bit in the integrated signalingformat.

As integrated signaling which may be similar to and used in place of theintegrated signaling (or CCC map) of Table 11 or 12, signaling of animproved RNTP/improved ABS type as shown in Table 13 below may bedefined.

TABLE 13 IE/Group Name Semantics description Enhanced RNTP Per PRB(and/or per subframe index (or Enhanced based on a subframe bitmap),ABS) map Enhanced RNTP (or Enhanced ABS) map(s) are listed, where eachenhanced RNTP (or Enhanced ABS) map consists of a (multi-level) RNTP (orEnhanced ABS or preference rating) value for each eNB (within an eNBgroup, e.g., CoMP cluster).

Hereinafter, an example of the integrated signaling of Table 13 will bedescribed with reference to FIG. 14.

FIG. 14 illustrates an improved RNTP map (or improved ABS map) signaledwith respect to a frequency/time resource.

For example, suppose that eNB1 is the sender eNB, and eNB2 is thereceiver eNB. In FIG. 14, the value M1 is interpreted as meaning thateNB1 sends a notice indicating that the power assignment thereof doesnot exceed the value M1. Value M2 is interpreted as meaning that eNB1recommends to eNB2 that power assignment of eNB2 not exceed the valueM2. Values M3, M4, and the like are interpreted as meaning that eNB1recommends to other eNBs that power assignment of other eNBs (eNB3,eNB4, . . . ) should not exceed the corresponding values (M3, M4, . . .) and that the receiver eNB2 performs scheduling thereof assuming thatother eNBs will operate according to the recommended power assignmentvalues.

In addition, in FIG. 14, candidate values or ranges which may be set topower assignment values M1, M2, M3, M4, . . . may be predefined orpreset. For example, a possible range of power assignment values may bebetween P_min and P_max, and each value means a maximum power thresholdvalue (i.e., indicating one value within the range means powerassignment not exceeding the indicated value). Indicating 0 as the powerassignment threshold value (e.g., predefining and indicating P_min=0)may mean that muting is performed.

The improved RNTP or improved ABS shown in FIG. 14 extends conventionalsignaling of RNTP or ABS to multi-level signaling, and includes not onlyinformation about the power assignment of the sender eNB but also arecommendation/request of power assignment for other eNBs.

In the examples of the present invention described above, identificationof specific eNBs such as eNB1, eNB2, eNB3, . . . may be predefined orpreconfigured in the form of a specific eNB set such as the CoMPcluster. Thereby, eNBs for which the values M1, M2, . . . of FIG. 14 areintended may be predefined, or an identifier indicating an eNB for whicheach power assignment value is intended (e.g., a cell ID of acorresponding eNB) may be signaled together with a power assignmentvalue with which the identifier is paired.

In addition, in the examples of the present invention described above,in order to more clearly indicate that various interpretations as aboveare applicable to the integrated signaling, a predetermined selector maybe defined. That is, the semantics by which the integrated signaling isto be interpreted may be announced by a value of the selector bit.

In the examples described above, Xn-signaling shown in Table 13 may belimited to be transmittable by only a specific eNB (e.g., the CCN orMacro-eNB) in the centralized coordination architecture.

In addition, an integrated signaling format configured by includingbenefit metric information of Table 12 in the example of Table 13 may bedefined as shown in Table 14 below.

TABLE 14 IE/Group Name Semantics description Enhanced RNTP Per PRB(and/or per subframe index based (or Enhanced on a subframe bitmap),ABS) map pair(s) of {Enhanced RNTP (or Enhanced ABS) map(s), benefitmetric} are listed, where each enhanced RNTP (or ABS) map consists of a(multi-level) RNTP (or ABS) value for each eNB (within an eNB group, Forexample, CoMP cluster).

Table 15 below shows an example of an integrated normal signalingformat, which is a generalization of the examples of Tables 7 to 14.

TABLE 15 IE/Group Name Semantics description Feature- {application type,resource map (ABS or integrated frequency/time map), associatedparameter backhaul set} are listed, where signalling “application type”will select (at least) (FIBS) one of the following applications {eICIC,CoMP, eIMTA, NAICS, . . .}, and “resource map” is a predefined form,e.g., ABS subframe (bitmap), frequency/time map, etc., and “associatedparameter set” is specifically defined based on each application type.

In Table 15, for the resource map, an enhanced inter-cell interferencecoordination (eICIC) ABS pattern signaling format (e.g., a 40-bit ABSpattern designed for eICIC) may be reused.

In addition, if the application type is CoMP, the “associated parameterset” may be configured in the form of a list of one or more elementsfrom a set of {NW-CSI-IM index(es), NW-CSI-RS index(es), NW-CSI-processindex(es), improved RNTP map(s) (or improved ABS map(s)), benefit metric(or utility metric, preference rating, priority map), precodinginformation containing a beam direction/coefficient, parameters (e.g.,CSI report, RSRP, SRS power, UPT, PF metric, QCI) used for NIB CoMPoperation}.

For other application types such as the eICIC, enhanced interferencemitigation & traffic adaptation (eIMTA), and network-assistedinterference cancellation and suppression (NAICS), a parameter setincluding one or more of parameters (e.g., the CoMP applicationtype-related parameters, precoding information, multi-level powerinformation, and modulation order information) associated with theapplication may be configured or indicated.

For example, if the “application type” is CoMP or eICIC, the “associatedparameter set” may include a CSI measurement parameter and CSI-IMmapping-related information.

If the “application type” is NAICS, the “associated parameter set” mayinclude a modulation order, CFI, PMI, RI, MCS, resource allocation, DMRSport, n^(DMRS) _(ID), transmission mode (TM), and RS configurationinformation. In addition, for NAICS, the associated parameters may beinterpreted as information applied for an indicated frequency/timeresource map.

The “application type” information may also be indicated by apredetermined index (e.g., 00, 01, . . . ), and the information to beincluded in the “associated parameter set” may be indicated according tothe index value. Alternatively, the “application type” information maybe defined as being optional. In this case, information to be includedin the “associated parameter set” or how the set is to be interpretedmay be set to a default. Alternatively, a specific “application type”(or a specific index indicating the application type) may be defined orconfigured to be implicitly indicated according to the informationconfiguration type of the “associated parameter set”.

For the Xn-signaling formats proposed in the examples described above,formats for higher layer signaling (e.g., RRC signaling) exchangedbetween an eNB and a UE may also be applied. For example, when the UEreceives RRC signaling, the UE may recognize an operation (ortransmission assumption) of eNBs in a CoMP cluster, and perform CoMPreception considering the recognized operation.

Additional Example 2 of Inter-NIB CoMP eNB Signaling

The following information may be signaled on an Xn interface (e.g., X2interface) between eNBs NIB CoMP:

-   -   One or more sets of CSI reports (RI, PMI, CQI) on individual        UEs;    -   One or more measurement reports (RSRP) on individual UEs;    -   SRS reception power for individual UEs;    -   User perceived throughput (UPT) for individual UEs;    -   Resource usage information according to each cell;    -   PF metrics for individual UEs;        -   Information of an improved RNTP type defined in the            frequency/time/power/space domain;    -   Improved ABS information defined in the power and space domain;    -   QCI;    -   Indication of a resource coordination result or resource        coordination request (resource allocation in the        frequency/time/power/space domain);    -   Information indicating configurations used for a reference        signal, CSI process and CSI-IM configuration;    -   Information indicating a coordination result or coordination        request for a reference signal configuration, CSI process and        CSI-IM configuration;

Preconditions for CoMP

To perform NIB CoMP operation, information on predeterminedpreconditions (e.g., information on configurations used for a referencesignal, CSI process and CSI-IM configuration) needs to be provided in aCoMP cluster. Although the reference signal configuration, CSI processand CSI-IM configuration are provided to a UE through UE-dedicated RRCsignaling, CSI-RS and CSI-IM configurations are preferably pre-subjectedto network-wise (NW) coordination by O&M (operation and maintenance) orbackhaul signaling support. For example, an NW CSI-IM index set may bepredefined in the CoMP cluster and indicate muting/non-muting or “don'tcare” operation of each eNB on each CSI-IM resource. In addition, someof the indexes of the NW CSI-IM index set may be selected and configuredfor a UE associated with a corresponding eNB through RRC signaling bythe eNB signaling.

To raise flexibility for operation of individual eNBs according to eachCSI-IM resource, multi-level power assignment and/or precodinginformation configuration for CB, for example, may be signaled in theCoMP cluster. Similar to the example of CSI-IM, an NW RS configurationindex, and an NW CSI process configuration index may be configured inthe CoMP cluster.

Integrated Signaling for Resource Coordination

Considering that the kinds of information necessary for NIB CoMPresource coordination have a common purpose (e.g., resource coordinationrequest/recommendation in the CoMP cluster or a resource coordinationresult/notice), signaling of the information is preferably simplifiedand unified.

The resource coordination request/recommendation provides elementinformation for CoMP scheduling from a member eNB to a CCN, and mayinclude, for example, one or more sets of CSI reports (RI, PMI, CQI) onindividual UEs, one or more measurement reports (RSRP) on individualUEs, SRS reception power for individual UEs, UPT for individual UEs,resource usage information according to each cell, QCI, PF metrics forindividual UEs, indication of a resource coordination request (resourceallocation in the frequency/time/power/space domain), indication of acoordination request for a reference signal configuration/CSIprocess/CSI-IM configuration.

The resource coordination result/notice is to send a notice of acoordination result from the CCN to member eNBs and may include, forexample, indication of a resource coordination result (resourceallocation in the frequency/time/power/space domain) and indication of acoordination result for a reference signal configuration/CSIprocess/CSI-IM configuration.

Of the two types of signaling as above, signaling for resourcecoordination request/recommendation preferably defines an integratedsignaling format rather than defining various different signalingformats.

In addition, the information about the “individual UEs” may notnecessarily be shared in a cluster. Instead, in view of the sender eNB,it may be more efficient for the information to include informationabout “a UE to be scheduled” on the specific frequency/time resourcemap. Each eNB performs final scheduling decision (i.e., finaldetermination of a UE to be scheduled) on its own. Sharing informationabout all possible UEs to be scheduled of an eNB with other eNBs maycause unnecessary overhead for information exchange, and thus sharingonly information about best (or representative) UEs is sufficient.

In the centralized coordination architecture, information such as CSIreport information, RSRP, SRS power, UPT, and QCI for each UE may not benecessarily needed. It may be only needed to share a preference ratingvalue (utility metric, PF metric, or benefit metric) for best orrepresentative UEs to be scheduled according to each frequency/timeresource. This is because sharing information in the CoMP cluster isintended for resource coordination between eNBs, not for finalscheduling determination of individual eNBs. Accordingly, a simplifiedpreference rating value (or benefit metric value) may be used.

Simplified preference rating information (or benefit metric information)about a specific frequency/time resource map is preferably signaledtogether with an indication of an assumed CoMP hypothesis. Herein, theCoMP hypothesis is an assumption on operation of eNBs in the CoMPcluster (e.g., eNB1 performs muting, and eNB2 does not perform muting),and may be expressed in a simple form using a predefined NW-CSI-IM indexor an explicit power assignment list for individual eNBs.

FIG. 15 illustrates a benefit metric signaled together with a CoMPhypothesis for a frequency/time resource map.

In FIG. 15, the CoMP hypothesis may be indicated by a power assignmentlist for individual eNBs. The power assignment list may be configured toexplicitly indicate the power assignment value for eNB1, the powerassignment value for eNB2, . . . , and the power assignment value foreNB N. Alternatively, the CoMP hypothesis may be indicated in a simplerform such as an NW CSI-IM index. That is, one index value may indicateoperation of individual eNBs.

The preference rating value may be defined as an integer between 0 and L(L>0). For example, L may be set to 100. The preference rating value maybe expressed as a level of preference in consideration of a schedulingbenefit which the sender eNB expects assuming that the indicated CoMPhypothesis is applied. Alternatively, the benefit metric value describedin FIG. 13 may be applied in place of the preference rating value.

Hereinafter, interpretation of an example of the integrated signalingformat of FIG. 15 will be described.

In the centralized coordination architecture, if the sender eNB is notthe CCN but a member eNB, the integrated signaling of FIG. 15 isinterpreted as indicating a resource coordination request/recommendationin view of the member eNB. Thereby, the CCN may perform coordinationdecision based on all information provided from member eNBs. Each membereNB may provide a plurality of signals, and each signal may includeinformation indicating a different preference rating value (or benefitmetric value) for a different CoMP hypothesis (hypothesis for operationsof the sender eNB and other eNBs).

If the sender eNB is the CCN in the centralized coordinationarchitecture, the integrated signaling of FIG. 15 is interpreted asindicating a resource coordination result/notice determined by the CCN,and all member eNBs receiving the signaling conform to details of thenotice. Specifically, each receiver eNB needs to maintain operation onthe indicated frequency/time resource with the same details (e.g., thetransmit power value, whether to perform muting, precoding, etc.) ofoperation on a CSI-IM resource indicated by an NW-CSI-IM indexindicating the CoMP hypothesis assumed in FIG. 15. Only in this case,may each eNB make a final UE scheduling decision thereof on theindicated frequency/time resource by directly applying the latest CSIfeedback report of the UE based on the corresponding CSI-IM resource onthe assumption that operation of other eNBs is guaranteed as indicated.In addition, according to this method, each eNB may select a type of asignal transmitted on the CSI-IM resource without restriction. Thereby,the CB type CoMP technique may be utilized on the NIB condition.

In FIG. 15, for a format in which an explicit power assignment list ofindividual eNBs (identified by cell ID indications of individual eNBs),the transmit power of a corresponding eNB on the indicatedfrequency/time resource should not exceed a value indicated as the powerthreshold value of the eNB. The power threshold may be set to differentlevels. If the corresponding signaling is transmitted from the CCN, thismay be interpreted as improved RNTP/ABS signaling including operation ofa plurality of eNBs.

If the sender eNB of the format of FIG. 15 is a CCN, the preferencerating information (or benefit metric information) may be omitted or setto a fixed value. This is because signaling from the CCN in thecentralized coordination architecture is interpreted as a resourcecoordination result/notice. That is, since the CCN functions to performresource coordination decision in consideration of preference ratinginformation (or benefit metric information) which the member eNBexpects, preference rating information (or benefit metric information)that the CCN expects does not need to be provided to the member eNB. Ifsignaling transmitted from the member eNB to the CCN and signalingtransmitted from the CCN to the member eNB are defined in an integratedsignaling format as in this embodiment, the preference ratinginformation (or benefit metric information) may be set to afixed/special value indicating that the signaling is the type of anotice/command of the resource coordination decision that the CCNtransmits to the member eNB, may be omitted, or may be reserved.

For the integrated signaling of FIG. 15, in the distributed coordinationarchitecture, most of the description given above of the case where thesender eNB is not the CCN in the centralized coordination architecturemay be applied. For example, if the sender is eNB1 and the receiver iseNB2, the integrated signaling of FIG. 15 is interpreted as a resourcecoordination request/recommendation including the preference ratingvalue of eNB1 from eNB1. The receiver eNB2 may consider the receivedinformation for scheduling decision thereof.

Specifically, eNB2 may consider that the information about operation ofthe sender eNB1 is guaranteed to be applied to eNB1 later. Thereby, thereceiver eNB2 may utilize a CSI feedback report of a relevant UE. Theinformation about the operation of the receiver eNB2 may be consideredwhen eNB2 operates in the best effort manner. In the distributedcoordination architecture, lots of such signaling may be exchanged, andthus the receiver eNB2 may also consider information about operation ofother eNBs in performing scheduling thereof. For example, the mostcommonly preferred CoMP hypothesis (i.e., a CoMP hypothesis to which alarge number of eNBs has assigned a higher preference rating value thanto the other CoMP hypotheses) may be used as an assumption on finalscheduling decision of the receiver eNB2.

Signaling Applied to Distributed Coordination Architecture

In the distributed coordination architecture, improved RNTP-typeinformation (e.g., a frequency/time/power/space domain) and improved ABSinformation (e.g., a power/space domain) may be signaled. Suchinformation is recognized as a notice of operation of the sender eNBrelated to the power level and/or beamforming information of the sendereNB on an indicated frequency/time resource.

In contrast with existing RNTP/ABS (almost blank subframe) signaling,the resource configuration granularity is extended to thetwo-dimensional domain of a frequency-time resource map, multi-levelpower assignment information is indicated, and indication information(e.g., precoding information) in the space domain is included insignaling.

The integrated signaling of FIG. 15 format may be applied to both thecentralized coordination architecture (e.g., the sender eNB is not theCCN) and the distributed coordination architecture and used to notify ofoperation of the sender eNB. Accordingly, the integrated signaling mayalso include improved RNTP/ABS signaling. The integrated signalingformat of FIG. 15 may also be used to request/recommend operation ofother eNBs. Accordingly, the improved RNTP/ABS type information may beviewed as signaling for subset information of the integrated signalingformat. That is, an information element for the preference rating valueand/or an information element requesting/recommending operation of othereNBs in the integrated signaling of FIG. 15 are designed as optionalelements, a flexible signaling format allowing the network operator tobe used both in the centralized coordination architecture and thedistributed coordination architecture may be defined.

However, if signaling applied to only the distributed coordinationarchitecture is introduced, the improved RNTP/ABS type informationsignaling may be separately defined, and the integrated signaling formatas shown in FIG. 15 may be defined as properly supporting thecentralized coordination architecture of NIB CoMP.

In this case, status report signaling (i.e., feedback information fromthe receiver eNB) about usage on the indicated frequency/time resourcemay be needed. For example, a feedback report on how much of theinformation indicated by the sender eNB is used for non-CoMP UE and CoMPUE scheduling is used may be sent. Similar to the existing ABS statusreport, the feedback information may be used when each eNB determinesthe next backhaul signaling in consideration of feedback informationfrom other eNBs.

Configuration Granularity for Xn-Signaling

In the examples described above, the benefit metric may be Xn-signaledin association with a CoMP hypothesis.

The CoMP hypothesis includes hypothetical resource allocation for atleast a receiver node in the time/frequency domain.

How to respond to the received CoMP hypothesis signaling depends onimplementation of the receiver eNB, or the receiver eNB may send thetransmitter node a feedback (e.g., YES/NO) indicatingacceptance/rejection of the hypothesis.

A configuration granularity and rate needed for the CoMP hypothesis inthe time/frequency domain may be given as follows. For example, the CoMPhypothesis may have a signaling period of a maximum T (T=5) ms. Inaddition, the CoMP hypothesis may be signaled in the form of a bitmap ina subframe unit identified by a subframe index defined based on thenumber of subframes equal to the signaling period, in a cell unitidentified by a cell ID in a coordination region (e.g., a CoMP cluster),or with a configuration granularity of one RB.

Herein, the signaling configuration granularity may be viewed as anexample of the specific time interval and/or specific band of 1-waysignaling and 2-way signaling for the SSPM.

Alternatively, the CoMP hypothesis may be signaled in the form of abitmap with a configuration granularity of one band rather than one RB.This example is implemented considering that the minimum configurationgranularity of CSI feedback of the UE is a subband unit. For the subbandwhich is a configuration granularity for Xn-signaling of the CoMPhypothesis, a transmitter node (i.e., a sender eNB) may deliver thesystem bandwidth thereof together with Xn-signaling for delivering theCoMP hypothesis or as separate Xn-signaling.

For example, the size of the subband according to the system bandwidthmay be defined as shown in Table 16 or 17 below.

TABLE 16 System Bandwidth Subband Size N_(RB) ^(DL) (k) 6-7 NA  8-10 411-26 4 27-63 6  64-110 8

TABLE 17 System Bandwidth Subband Size Bandwidth N_(RB) ^(DL) k (RBs)Parts (J) 6-7 NA NA  8-10 4 1 11-26 4 2 27-63 6 3  64-110 8 4

Table 16 defines a subband size (in units of RB) according to the systembandwidth, and Table 17 defines a relationship among a DL systembandwidth, a bandwidth part, and a subband size (in units of RB) in thecase of periodic CSI reporting.

Alternatively, the subband size defined according to the systembandwidth may be defined as shown in Table 18 below.

TABLE 18 System Bandwidth Subband Size N_(RB) ^(DL) k (RBs) M 6-7 NA NA 8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 6

Table 18 defines a relationship among a DL system bandwidth, a bandwidthpart, and a subband size (in units of RB) in the case of aperiodic CSIreporting. Compared to the example of Table 16 or 17, the subband sizesare small in the same system bandwidth, and thus the configurationgranularity of the subband may be understood as being finer than that ofthe previous examples.

Using the subband configuration granularity, the frequency domainconfiguration granularity of the CoMP hypothesis may be defined.

In addition, CSI information about a UE set may be Xn-signaled. Aconfiguration granularity for this signaling may be defined as a subbandconfiguration granularity shown in Table 16, 17 or 18.

For example, one or more sets of CSI information may be Xn-signaled fora set of UEs. A necessary rate for exchange of the one or more sets ofCSI information may be given as follows. For example, a signaling periodof up to 5 ms may be given, and aperiodic CSI reporting providedaccording to the request from an eNB may be supported. In addition, oneor more sets (up to 4 sets) of CSI information and an assumption on aCSI process (identified by a cell-specific CSI process ID) associatedwith each CSI information set may be signaled in a subframe unitidentified by a subframe index defined based on the number of subframesequal to the signaling period, in a cell unit identified by a cell ID,in the subband unit identified by a subband index (wherein the size ofthe subband may be a size listed in Table 16, 17 or 18), or in a UE unitidentified by a UE ID.

In order to signal an assumption for a CSI process associated with theCSI information, information (e.g., one NZP CSI-RS resource, one CSI-IMresource, or the like) contained in each CSI process ID set for the UEmay be signaled along with Xn-signaling for the CSI information set orseparately. Alternatively, while CSI process configuration informationfor each individual UE and a corresponding CSI process ID arepre-exchanged or pre-known among a plurality of eNBs (e.g., a CSIprocess ID such as the “cell-specific CSI process ID” uniquelyidentifiable between eNBs by OAM (Operation And Management) in anetwork-wise (NW) manner is preconfigured), a CSI process ID (i.e.,NW-CSI-process ID) only needs to be signaled for an “assumption for anassociated CSI process”.

In order to signal the “assumption for a CSI process associated witheach CSI information set”, a format for signaling an assumption for aCoMP hypothesis (regardless of the frequency/time resource configurationgranularity) may be used. That is, the assumption may be extended tosignal that the CSI information set corresponds to a specific CoMPhypothesis. Herein, while the original CoMP hypothesis is defined basedon the frequency/time resource configuration granularity, the CSIinformation set is signaled based only on the power assignment status ofeach eNB (i.e., a CoMP hypothesis is needed only for the purpose ofindicating a cell to perform muting as in the case of a CSI-IMconfiguration included in a CSI process, and not needed to expressoperation of each cell on a frequency/time resource). Accordingly, insignaling a CSI information set associated with a CoMP hypothesis, adefinition of “Regardless of the frequency/time resource configurationgranularity” may be defined.

As an additional example of a configuration granularity and rate of aCoMP hypothesis, a CoMP hypothesis signaling period (i.e., T ms) may beset in consideration of feedback periods set for individual UEs. Forexample, the T value may not be predefined, but may be determined andsignaled (along with signaling of a CoMP hypothesis and benefit metricor separately) by the sender eNB. If the value of T is delivered everytime the sender eNB transmits signaling including a CoMP hypothesis andbenefit metric (or once per a plurality of signals), this may indicatethat every time the value of T changes, signaling including the CoMPhypothesis and benefit metric is transmitted with the changedperiodicity of T ms. That is, if the value of T is not included, thismay indicate that the value of T as previously signaled is applied. Forexample, if a changed value T2 is signaled after a value T1 is signaled,this means that signaling including a CoMP hypothesis and benefit metricis transmitted according to a period T2 until another changed value T3is signaled.

Alternatively, the period T of signaling including a CoMP hypothesis andbenefit metric may be signaled as requested/designated by the receivereNB. This may mean that the receiver eNB signals a desired period ofreceiving signaling including a CoMP hypothesis and benefit metric.Thereby, the sender eNB may transmit signaling in consideration of suchvalue of T. Alternatively, the sender eNB may not need to reflect thevalue T1 desired by the receiver eNB. Instead, the sender eNB maytransmit signaling according to period T2 which the sender eNB desiresin consideration of the value T1. If signaling is transmitted accordingto period T2 different from the value T1 desired by the receiver eNB,information about the signaling period T2 may be transmitted to thereceiver eNB.

In a situation in which signaling including a CoMP hypothesis, CSIinformation set and benefit metric is transmitted according to period T,the CSI information set includes information about a set of UEs, and theUEs included in the set of UEs may change at every signalingtransmission time. This is because each UE may have a different feedbackperiod. For example, if the feedback period of UE1 is 5 ms, and thefeedback period of UE2 is 10 ms, signaling including the CSI informationset may be transmitted with T set to 5 ms. Thereby, a “set of UEs”related to a CSI information set at a specific transmission time mayinclude only UE1, and a “set of UEs” related to a CSI information set atthe next transmission time after 5 ms may include only UE2.

CB Technique

FIG. 16 illustrates a CB technique.

CB is a technique for minimizing interference of a beam transmitted froma TP participating in CoMP that affects a UE which another TP serves.For example, as shown in FIG. 16, to perform data transmission to UE2associated with TP2, TP2 may select a precoder (e.g., PMI2) allowingbeam avoidance such that interference affecting UE1 served by TP1 isminimized. To this end, TP1 and TP2 are required to exchange changestate information such as PMI through Xn-signaling in an NIBenvironment.

1-Way Xn-Signaling for Initiation of CB

Xn-signaling for CB may be defined to be broadcast (or unicast ormulticast to one or more other TPs) by a specific TP (e.g., TP2 of FIG.16) in 1-way.

In this case, the information provided by a TP transmitting Xn-signalingmay be a message informing of a PMI which the TP is to apply in a“specific band” in a “specific time interval”.

The PMI information contained in the Xn-signaling may be a single PMI ora PMI set including two or more PMIs. Other TPs receiving the PMIinformation may select and schedule UEs which will be affected byminimum interference from a beam formed by the PMI sete. Alternatively,TP1 may compare the “PMI set” contained in Xn-signaling transmitted byTP2 and the optimum PMI2 measured by UEs with respect to TP2, and thenselect, as scheduling targets, UE(s) reporting PMI2 most orthogonal tothe “PMI set”. Then, a UE minimizing interference from TP2 may bescheduled. Thereby, signal quality may be improved by beam avoidance.

Herein, the “specific time interval” may have a value indicated by apredetermined time unit (e.g., subframe). In addition, the “specifictime interval” may be expressed as time information (e.g., continuous ordiscontinuous time information configured in the form of a subframebitmap) indicating the start time and end time of CB based on areference time that is clearly known between TPs. In addition to theaforementioned form of a subframe bitmap, a time (e.g., a specificsubframe index) at which the “specific time interval” starts may beexplicitly indicated, or the number of cycles completed by the subframebitmap before the “specific time interval” ends at a given time (e.g., aspecific subframe index) may be explicitly indicated.

To express such “specific time interval”, a frame number (e.g., a systemframe number (SFN)) at which a CoMP operation (muting/non-muting, etc.)is applied (or started) may be used. For example, the CoMP operation maybe applied in a radio frame explicitly indicated by an SFN contained inXn-signaling. In this case, the frame number (e.g., SFN) may be definedbased on timing of a TP transmitting Xn-signaling. Alternatively, if theTP transmitting Xn-signaling is aware of information about timing of aTP receiving the Xn-signaling, the SFN value may be set to a value basedon timing of the TP receiving the Xn-signaling and transmitted.

In addition, the “specific band” may be set to a value expressed by apredetermined frequency unit (e.g., RB unit).

2-Way Xn-Signaling for Initiation of CB

Xn-signaling for CB may be defined as 2-way signaling implemented in amanner that TP1 makes a request to TP2 for performing CB based on aspecific PMI set (information about one or more PMIs) CB, and TP2 sendsa response to TP1. In this case, the response message transmitted by TP2may be multicast/broadcast to TP1 and other TPs (e.g., TP3, TP4, . . .), or may be individually unicast to TP1 and other TPs by TP2.

Herein, the information contained in the request message transmitted byTP1 may be a message requesting that TP2 perform CB using a specific PMIset (information about one or more PMIs) for a “specific band” in a“specific time interval”.

For the “specific time interval” and “specific band”, the same featuresof 1-way Xn-signaling for CB described above may be applied.

In this example, a “specific condition” for transmission of the requestmessage from TP1 may be defined.

For example, TP1 and TP2 may compare traffic load situations thereof(through exchange of Xn-signaling), and if the difference between theload situations is greater than or equal to a predetermined referencevalue, this may satisfy a condition for transmitting the requestmessage.

Herein, only if the value of the load situation of TP2 is well below apredetermined reference value, the request may be allowed.Alternatively, if the value of the load situation of TP2 is greater thanthe predetermined reference value, TP2 may reject the delivered request.

The “specific condition” may be defined such that priorities are presetbetween the TPs (e.g., TP1 may be preset as a master, and TP2 may bepreset as a slave), and thus when TP1 sends the request according to thepriorities, TP2 must conform to the request.

If TP1 is pre-provided with information pre-confirming that TP2 willaccept the request, through information such as the loading information,information about one or more CSI-RS configurations, information aboutone or more CSI-IM (or IMR) configurations, or DMRS configurationinformation, which is pre-exchanged through Xn-signaling, the CBoperation may be initiated simply by a muting request for CB which TP1sends to TP2 (namely, without a response from TP2).

If a specific condition for transmission of the request message isdefined as above, and the request message is transmitted from TP1 as thecondition is satisfied, TP2 receiving the request message may accept therequest. The case in which TP2 should obey the request of TP1 if aspecific condition is satisfied (or the case in which TP2 obeys therequest without sending a response message to TP1) may be calledconditional 1-way Xn-signaling.

Xn-Signaling During CB Operation

If CB is initiated through 1-way or 2-way Xn-signaling in a specificband in a specific time interval, CB may be defined as automaticallyending when the time interval ends. Alternatively, the time interval maybe extended through additional Xn-signaling (e.g., 1-way signaling or2-way signaling) before the time interval ends. The information aboutthe extended time interval may be updated with new type timeinformation, and the band information may be updated with new type bandinformation.

Xn-Signaling for Feedback for CB

Xn-signaling for feeding back usage information about whether PDSCHtransmission for scheduling a CoMP UE in consideration of the CB (e.g.,MCS configuration in consideration of CB) has been performed may beadditionally defined in or after the CB time interval.

By recognizing the usage indicating whether a time interval and band inwhich neighboring TPs have conducted CB have been actually used inscheduling a corresponding CoMP UE, unnecessary application of the CBoperation may be prevented.

Combination of SSPS and CB

For the CB operation described above, the TP transmitting the PDSCH maybe basically a fixed TP (e.g., TP1 of FIG. 16), and neighboring TPs(e.g., TP2) may use a PMI to which beam avoidance according to CB isapplied. Herein, CB may be combined with semi-static point switching(SSPS) such that the TP transmitting a PDSCH is changed by SSPS (to, forexample, TP2) (e.g., TP1 and TP2 alternately transmit the PDSCH on aspecific resource), and neighboring TPs (e.g., TP1) may apply CB. Assuch, functions of TP1 and TP2 may be switched.

FIG. 17 is a flowchart illustrating a signaling method according to anembodiment of the present invention.

In FIG. 17, a first network node and a second network node are networknodes participating in or involving in CoMP on an NIB network. Forexample, the first and second network nodes may be network nodesparticipating in CoMP in the distributed coordination architecture, andmay correspond to a member node and a CCN in the centralizedcoordination architecture.

In step S1710, the first network node may transmit first type signalingto the second network node. The first type signaling may include one ormore CoMP hypotheses (i.e., a first CoMP hypothesis) in view of thefirst network node, and additionally include a benefit metric for eachCoMP hypothesis. The first type signaling may be interpreted as resourcecoordination request/recommendation signaling.

In step S1720, the first network node may receive second type signalingfrom the second network node. The second type signaling may include oneor more CoMP hypotheses (i.e., a second CoMP hypothesis) in view of thesecond network node, and additionally include a benefit metric for eachCoMP hypothesis. In the distributed coordination architecture, thesecond type signaling may be resource coordinationrequest/recommendation signaling in view of the second network node, orresource coordination result/notice signaling for the first networknode.

In the centralized coordination architecture, the first type signalingmay be resource coordination request/recommendation signaling sent fromthe member node to the CCN, and the second type signaling may beresource coordination result/notice signaling sent from the CCN to themember node.

The first and second type signaling may be configured by an integratedsignaling format (or information element format) proposed in the presentinvention. That is, the first and second type signaling may use the samesignaling format, and be identified/distinguished by the content of thesignaling. For example, a specific bit of the integrated signalingformat may function to identify the first type/second type signaling(e.g., benefit metric information has a meaning only in the first typesignaling in the centralized coordination architecture, and therefore abit corresponding to the benefit metric information may be set to aspecial value in the second type signaling to indicate the second typesignaling).

Each of the first and second CoMP hypotheses may include informationabout transmission assumptions for the respective CoMP network nodesaccording to CSI-process indexes. That is, transmit power levels(including whether to perform muting) of the respective CoMP networknodes on the assumption of a specific CSI-process and precodinginformation may constitute CoMP hypothesis information. Herein, aCSI-process index may be defined as a value that is uniquely identifiedin a network (i.e., as a network-wise (NW) index). Further, an NZPCSI-RS index and CSI-IM index constituting the CSI-process may bedefined as an NW-NZP-CSI-RS index and NW-CSI-IM index, respectively.

Each of the CoMP hypotheses may be defined as a “CoMP hypothesis set”together with ID (e.g., cell ID) information for identifyingcorresponding CoMP network nodes. That is, information explicitlyindicating a cell for which a CoMP hypothesis is intended may beincluded in the first or second type signaling.

Regarding the method described above with reference to FIG. 17, variousembodiments of the present invention described above may beindependently applied or two or more of the embodiments may besimultaneously applied. Redundant description of the embodiments will beomitted.

While FIG. 17 illustrates operations for the exemplary method in seriesfor simplicity, this is not intended to limit the order in which theoperations are performed. Operations may be performed simultaneously orin a different order if necessary. Further, not all steps illustrated inFIG. 17 are essential to implementation of the proposed method of thepresent invention.

FIG. 18 is a diagram illustrating configuration of a network nodeaccording to a preferred embodiment of the present invention.

Referring to FIG. 18, a network node 100 may include a transceiver 110,a processor 120, a memory 130, and a plurality of antennas. Thetransceiver 110 may receive various signals, data and information fromexternal devices (e.g., a UE). The transmit module 12 may exchangevarious signals, data and information with an external device (e.g., aUE) or another network node. The processor 120 may control overalloperation of the network node 100. The antennas mean that the networknode 100 supports MIMO transmission and reception.

According to an embodiment, the network node 100 may be configured toperform or support CoMP transmission on a wireless communicationnetwork. The processor 120 may be configured to transmit first typesignaling containing one or more first CoMP hypothesis sets from a firstnetwork node to a second network node, using the transceiver 110. Inaddition, the processor 120 may be configured to receive second typesignaling containing one or more second CoMP hypothesis sets from thesecond network node at the first network node, using the transceiver110.

The processor 120 of the network node 100 may additionally function tocomputationally process information which the network node 100 hasreceived from the outside, and the memory 130 may store thecomputationally processed information for a predetermined time and maybe replaced by an element such as a buffer (not shown).

The network node 100 may correspond to an eNB, a TP and the like thatparticipate in CoMP operation.

Regarding the specific configuration of the network node 100, variousembodiments of the present invention described above may beindependently applied or two or more of the embodiments may besimultaneously applied. Redundant description of the embodiments will beomitted.

In the embodiments described above, an eNB has been mainly given as anexample of a DL transmission entity or UL reception entity, and a UE hasbeen mainly given as an example of a UL reception entity or ULtransmission entity. However, the scope of the present invention is notlimited thereto. For example, description of the eNB may also be appliedwhen a cell, AP, AP group, RRH, transmission point, reception point,access point, relay or the like serves as a DL transmission entity or ULreception entity with respect to the UE. In addition, the principle ofthe present invention described through various embodiments of thepresent invention may be applied even in the case where the relay servesas a DL transmission entity or UL reception entity with respect to theUE or in the case where the relay serves as a UL transmission entity orDL reception entity with respect to the eNB.

The embodiments of the present invention may be implemented throughvarious means, for example, hardware, firmware, software, or acombination thereof.

When implemented as hardware, a method according to embodiments of thepresent invention may be embodied as one or more application specificintegrated circuits (ASICs), one or more digital signal processors(DSPs), one or more digital signal processing devices (DSPDs), one ormore programmable logic devices (PLDs), one or more field programmablegate arrays (FPGAs), a processor, a controller, a microcontroller, amicroprocessor, etc.

When implemented as firmware or software, a method according toembodiments of the present invention may be embodied as a module, aprocedure, or a function that performs the functions or operationsdescribed above. Software code may be stored in a memory unit andexecuted by a processor. The memory unit is located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

Preferred embodiments of the present invention have been described indetail above to allow those skilled in the art to implement and practicethe present invention. Although the preferred embodiments of the presentinvention have been described above, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention. For example, those skilled in the art may use a combinationof elements set forth in the above-described embodiments. Thus, thepresent invention is not intended to be limited to the embodimentsdescribed herein, but is intended to have the widest scope correspondingto the principles and novel features disclosed herein.

The present invention may be carried out in other specific ways thanthose set forth herein without departing from the essentialcharacteristics of the present invention. Therefore, the aboveembodiments should be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. The present invention is not intendedto be limited to the embodiments described herein, but is intended tohave the widest scope consistent with the principles and novel featuresdisclosed herein. In addition, claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention described above are applicableto various mobile communication systems.

What is claimed is:
 1. A method for performing Coordinated Multi-Point(CoMP) transmission in wireless communication system, the methodcomprising: receiving, by a second eNodeB from a first eNodeB via anon-ideal backhaul (NIB) link, CoMP information comprising at least oneCoMP hypothesis and at least one benefit metric, wherein each of the atleast one benefit metric is associated with one of the at least one CoMPhypothesis, wherein the at least one CoMP hypothesis compriseshypothetical resource allocation information indicating a time-frequencyresource, and wherein each of the at least one benefit metric has aquantized value of a benefit expected for CoMP scheduling correspondingto the one of the at least one CoMP hypothesis associated with thebenefit metric; and performing, by the second eNodeB, CoMP schedulingfor a user equipment (UE) based on the at least one CoMP hypothesis andthe at least one benefit metric.
 2. The method according to claim 1,wherein the CoMP information comprises one or more identifications (IDs)of a cell related to the at least one CoMP hypothesis.
 3. The methodaccording to claim 1, wherein the second eNodeB is one of a plurality ofeNodeBs that receives the CoMP information from the first eNodeB.
 4. Themethod according to claim 1, wherein the CoMP information comprises atleast one of a time interval or a frequency band for a CoMPtransmission.
 5. The method according to claim 4, wherein the CoMPinformation comprises a starting frame number of the CoMP transmission.6. The method according to claim 1, wherein the CoMP information istransmitted using X2 interface between the first eNodeB and the secondeNodeB.
 7. The method according to claim 1, wherein the time-frequencyresource corresponds to a Physical Resource Block (PRB).
 8. The methodaccording to claim 1, further comprising: transceiving information withthe UE based on the scheduling information generated in consideration ofthe at least one CoMP hypothesis.
 9. The method according to claim 1,wherein the hypothetical resource allocation information indicating atime-frequency resource comprises an eNodeB transmission parameter. 10.The method according to claim 1, wherein the at least one CoMPhypothesis comprises at least two different hypotheses, each containingrespective hypothetical resource allocation information indicating ahypothesis-specific time-frequency resource.
 11. An eNode B apparatusfor performing Coordinated Multi-Point (CoMP) transmission in wirelesscommunication network, the apparatus comprising: a transceiver; and aprocessor configured to receive, from another eNodeB via a non-idealbackhaul (NIB) link, CoMP information comprising at least one CoMPhypothesis and at least one benefit metric, wherein each of the at leastone benefit metric is associated with one of the at least one CoMPhypothesis, wherein the at least one CoMP hypothesis compriseshypothetical resource allocation information indicating a time-frequencyresource, and wherein each of the at least one benefit metric has aquantized value of a benefit expected for CoMP scheduling correspondingto the one of the at least one CoMP hypothesis associated with thebenefit metric; and perform CoMP scheduling for a user equipment (UE)based on the at least one CoMP hypothesis and the at least one benefitmetric.
 12. The eNode B apparatus according to claim 11, wherein theprocessor is further configured to transceive information with the UEbased on the scheduling information generated in consideration of the atleast one CoMP hypothesis.